A synonym is a word that has the same or nearly the same meaning as another word. For example, "beautiful" and "attractive" are synonyms because they both refer to someone or something that is pleasing to the eye. Synonyms can be found in every part of speech, including nouns, verbs, adjectives, adverbs, and prepositions.

An antonym, on the other hand, is a word that has the opposite meaning of another word. For instance, "good" and "bad" are antonyms because they have opposite meanings. Antonyms can also be found in every part of speech.

Understanding synonyms and antonyms is helpful when using a dictionary or thesaurus. A words entry often lists both synonyms and antonyms to help with writing. Familiarity with synonyms and antonyms can also be helpful in answering questions and choosing the most appropriate word to convey ideas.