synonym — a word that has the same or nearly the same meaning as another word.
『速い』の同義語には『迅速』や『早い』があるが、文脈で使い分けが必要だ。
Synonyms for 'hayai' (fast) include 'jinsoku' and 'hayai' (another kanji), but you need to choose based on context.
辞書で同義語を調べて表現の幅を広げよう。
Look up synonyms in a dictionary to broaden your expressive range.