How to say "optional" in Japanese

• 任意にんいCommon
  no-adjective, na-adjectiveCovers 'optional' in the sense of 'not required; at one's discretion', e.g. a field on a form you may fill in or leave blank. It can also mean 'arbitrary' or 'random', so rely on context.
• 随意ずいいCommon
  na-adjective, nounFits 'optional' when something is voluntary and left to each person, as when a notice says participation or attendance is up to the individual; the emphasis is on free choice.
  随意ずいいに退席たいせきしてかまいません。↗

  You may leave your seat at will.

Use 任意 for the plain 'optional' sense of something not required, such as a form field you may skip; use 随意 when stressing that an action like attendance or participation is voluntary, a matter of free choice.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 任意にんいoptional
• 随意ずいいvoluntary
• オプショナルoptional
• 任意信号にんいしんごうoptional
• 選択的せんたくてきselective
• 随意的ずいいてきvoluntary
• 参加自由さんかじゆうoptional (to participate in)
• 自由参加じゆうさんかoptional (to participate in)