Antonym — a word that has the opposite meaning of another word; a grammatical/lexical term.
「暑い」の反義語は「寒い」だ。
The antonym of "hot" is "cold."
この問題では、反義語を二つずつ挙げなさい。
In this exercise, list two antonyms each.
辞書の反義語欄には、反意語や対義語も合わせて載っていることが多い。
Dictionaries' antonym entries often also include related terms like contraries and opposites.