Lexicon in NLP

Internship at OpenGenus

In this article at OpenGenus, we will dive into the concept of lexicon in NLP, explore its importance, implementation, applications, and its role in various NLP tasks.

Table of content

  1. Introduction
  2. What is lexicon?
  3. Components of a Lexicon
  4. Lexical Semantics
  5. Applications of Lexicon in NLP
  6. A Simple Implementation
  7. Conclusion

Alright, Let's get started.


In the realm of Natural Language Processing (NLP), the analysis and understanding of human language play a crucial role. One of the fundamental components in NLP is the lexicon, which forms the building blocks for processing and interpreting textual data. The lexicon, also known as a vocabulary or wordbook, holds a significant position in NLP tasks, enabling algorithms to derive meaning from words in a computational manner. .

What is lexicon?

The lexicon refers to the collection of words, phrases, or symbols in a specific language. It encompasses the vocabulary of a language and includes various linguistic attributes associated with each word, such as part-of-speech tags, semantic information, pronunciation, and more. It serves as a comprehensive repository of linguistic knowledge, enabling NLP systems to process and understand natural language text.

Components of a Lexicon

A lexicon comprises several components that provide rich information about words and their properties. These components include:

  1. Words and their Meanings:
    The core component of a lexicon is the listing of words, each associated with its corresponding meaning(s). This provides the fundamental building blocks for language understanding.

  2. Part-of-Speech (POS) Tags:
    POS tags assign grammatical categories to words, such as noun, verb, adjective, adverb, and more. POS tags play a vital role in syntactic analysis and help disambiguate word meanings based on their context.

  3. Pronunciation:
    Lexicons often include information about the pronunciation of words, helping in tasks such as text-to-speech synthesis and speech recognition.

  4. Semantic Information:
    Some lexicons include semantic attributes associated with words, such as word senses, synonyms, antonyms, and hypernyms. These semantic relationships enable algorithms to infer deeper meaning from text.

Lexical Semantics

Lexical Processing encompasses various techniques and methods used to handle and analyze words or lexemes in natural language. It involves tasks such as normalizing word forms, disambiguating word meanings, and establishing translation equivalences between different languages. Lexical processing is an essential component in many language-related applications, including information retrieval, machine translation, natural language understanding, and text analysis.

Collectively, the three concepts of Lexical Normalization, Lexical Disambiguation, and Bilingual Lexicons are often referred to as Lexical Processing or Lexical Semantics.

  1. Lexical Normalization:
    Lexical normalization, also known as word normalization or word standardization, is the process of transforming words or phrases into their canonical or base form. It helps in handling variations in word forms to improve text analysis and natural language processing tasks. Techniques used in lexical normalization include stemming, lemmatization, and handling abbreviations or acronyms.

  2. Lexical Disambiguation:
    Lexical disambiguation aims to resolve the ambiguity present in natural language. It involves determining the correct meaning or sense of a word in a given context. This is important because many words in natural language have multiple meanings, and understanding the intended sense is crucial for accurate language processing. Techniques such as part-of-speech tagging, semantic role labeling, and word sense disambiguation algorithms are employed for lexical disambiguation.

  3. Bilingual Lexicons:
    Bilingual lexicons are linguistic resources that provide translation equivalents between words or phrases in different languages. They facilitate the process of translation and language understanding tasks by mapping words or phrases from one language to another. Bilingual lexicons can be manually curated or automatically generated using various techniques, including statistical alignment models, parallel corpora, machine learning, and bilingual dictionaries.

In summary, lexical normalization focuses on transforming words into their standardized forms, lexical disambiguation deals with resolving the ambiguity of words in context, and bilingual lexicons assist in translating words or phrases between different languages. These concepts play important roles in natural language processing, machine translation, and cross-lingual applications.

Applications of Lexicon in NLP

The lexicon finds extensive applications in various NLP tasks, contributing to the advancement of language processing algorithms. Here are a few key applications:

  1. Sentiment Analysis:
    Lexicons play a crucial role in sentiment analysis, where the goal is to determine the sentiment expressed in a given text. Lexicons contain sentiment scores or polarity labels associated with words. For example, the word "happy" might have a positive sentiment score, while "sad" could have a negative sentiment score. Implementations involve using lexicons to assign sentiment scores to words in a text and aggregating them to determine the overall sentiment of the text.

  2. Text Classification:
    Lexicons serve as valuable resources for text classification tasks. Lexicons can provide features for classification algorithms, aiding in better feature representation and decision-making. For example, a lexicon might contain words associated with specific topics or domains. Implementations involve incorporating lexicon-based features into classification algorithms to improve the accuracy of text classification.

  3. Machine Translation:
    Lexicons are utilized in machine translation systems to provide translation equivalents for words or phrases. For example, a lexicon might contain mappings between English and French words. Implementations involve leveraging the lexicon to translate words or phrases during the translation process.

  4. Word Sense Disambiguation:
    Lexicons with semantic information aid in word sense disambiguation, where the correct meaning of a word in a specific context needs to be determined. For example, a lexicon might contain multiple senses of the word "bank" (financial institution vs. river bank). Implementations involve using the lexicon to disambiguate the correct sense based on the context in which the word appears.

  5. Named Entity Recognition (NER):
    Lexicons are used in NER to identify and classify named entities such as person names, locations, organizations, etc. For example, a lexicon might contain a list of known organization names. Implementations involve matching the words in a text with the entries in the lexicon to identify and extract named entities.


Here's a simple implementation example using Python and the NLTK (Natural Language Toolkit) library to showcase how lexicons can be utilized for sentiment analysis:

import nltk
from nltk.corpus import opinion_lexicon

def analyze_sentiment(text):
    positive_words = set(opinion_lexicon.positive())
    negative_words = set(opinion_lexicon.negative())
    # Tokenize the input text into individual words
    tokens = nltk.word_tokenize(text)
    # Count the number of positive and negative words in the text
    positive_count = sum(1 for word in tokens if word in positive_words)
    negative_count = sum(1 for word in tokens if word in negative_words)
    # Determine the sentiment based on the word counts
    if positive_count > negative_count:
        sentiment = "Positive"
    elif positive_count < negative_count:
        sentiment = "Negative"
        sentiment = "Neutral"
    return sentiment

# Test the sentiment analysis function
text = "I really enjoyed the movie. It was fantastic!"
sentiment = analyze_sentiment(text)
print("Sentiment:", sentiment)

In this implementation, the NLTK library is used to access the opinion lexicon, which is a lexicon containing lists of positive and negative words. The analyze_sentiment function takes a piece of text as input and tokenizes it into individual words using NLTK's word_tokenize function. It then counts the number of positive and negative words in the text by checking if each word is present in the positive and negative word sets obtained from the opinion lexicon. Based on the word counts, it determines the sentiment as positive, negative, or neutral.

Note that this is a simplified implementation for demonstration purposes. In practice, more advanced techniques, such as handling negations, considering contextual information, or using machine learning models, may be employed to improve the accuracy of sentiment analysis. Nonetheless, this example illustrates how lexicons can be used as a resource for sentiment analysis tasks.


The lexicon serves as a critical component in Natural Language Processing, enabling algorithms to understand, analyze, and process human language effectively. With its collection of words, meanings, linguistic attributes, and semantic relationships, the lexicon acts as a valuable resource for various NLP tasks. From sentiment analysis to machine translation, lexicons play a pivotal role in advancing language processing algorithms. As research and development in NLP continue, further advancements in lexicon construction and enrichment will contribute to more accurate and context-aware language understanding, driving the progress of natural language processing technologies.