import nltk
from nltk.corpus import wordnet

synonyms = []

for syn in wordnet.synsets('book'):
        for lemma in syn.lemmas():
            synonyms.append(lemma.name())

print(synonyms)
>>['book', 'book', 'volume', 'record', 'record_book', 'book', 'script', 'book', 'playscript', 'ledger', 'leger', 'account_book', 'book_of_account', 'book', 'book', 'book', 'rule_book', 'Koran', 'Quran', "al-Qur'an", 'Book', 'Bible', 'Christian_Bible', ..]

len(synonyms)
 >>38