WordNet is a dictionary for programs: words are grouped into sets of synonyms (synsets) with definitions, and linked to antonyms and broader or narrower words.

Python

from nltk.corpus import wordnet

syn = wordnet.synsets("book")
print(syn[0].definition())      # a written work or composition that has been published (printed on pages bound together)
print(syn[0].name())            # book.n.01

Synonyms

Python

from nltk.corpus import wordnet
synonyms = []
for s in wordnet.synsets("happy"):
    for lemma in s.lemmas():
        synonyms.append(lemma.name())
print(sorted(set(synonyms)))    # ['felicitous', 'glad', 'happy', 'well-chosen']

Antonyms

Python

from nltk.corpus import wordnet
antonyms = {a.name() for s in wordnet.synsets("healthy") for l in s.lemmas() for a in l.antonyms()}
print(sorted(antonyms))         # ['unhealthy']

Call	Gives
`wordnet.synsets(word)`	Every sense of the word
`synset.definition()` / `.examples()`	Its meaning / example sentences
`synset.lemmas()`	The words in that sense (synonyms)
`lemma.antonyms()`	Opposites
`synset.hypernyms()`	Broader terms (dog → canine)