GRE TOEFL IELTS optional Definition Not required; left to personal choice. 日本語 必須ではない; 個人的な選択に任せる Example "Wearing a hat is optional during the tour." Sign in to save GRE PDF — $25 TOEFL PDF — $25 IELTS PDF — $25 ← option optometrist → Study tips featuring "optional" TOEFL Academic Vocabulary: Study by Topic Boost Your IELTS Writing With Precise Vocabulary Related words GRE awe GRE smithereens GRE abacus SAT abase GRE abash GRE abate GRE abbreviate GRE abbreviation SAT abdicate SAT abdomen GRE abduct GRE aberrant