How to Say "Optional" in Japanese

任意

nin'i[ɲ̟ĩɰ̃i]

The English word "optional" is translated into Japanese as 任意 (nin'i).

任意 is used to express the idea that something is optional or voluntary.

Meaning: not compulsory (adj)

How do you pronounce it?

nin'i

The word 任意 is used in mathematics to describe an 'arbitrary' value. In this context, it means any value can be chosen without restriction.
In the phrase 任意同行, which describes a 'voluntary' police accompaniment, the word 任意 is used even though the social pressure to comply makes it feel compulsory.
While 任意 is the formal way to say 'optional', in everyday digital menus or forms, you are much more likely to see the Katakana word オプション, which is a direct loanword from the English 'option'.

それはえらべるから、自由やな
That's optional, so it's up to you.
この項目は任意です。
Kono kōmoku wa nin'i desu.
This item is optional.
参加は任意となります。
Sanka wa nin'i to narimasu.
Participation is optional.
提出は任意ですが、お願いします。
Teishutsu wa nin'i desu ga, onegaishimasu.
Submission is optional, but please do it.

Kenta and Misaki are talking about a company workshop.

健太 Kenta

明日の研修は任意なの？
Ashita no kenshū wa nin'i na no?
Is tomorrow's workshop optional?
美咲 Misaki

うん、自由参加だよ。
Un, jiyū sanka da yo.
Yeah, it's free participation.
健太 Kenta

じゃあ、美咲さんは行く？
Jā, Misaki-san wa iku?
Then, are you going, Misaki?
美咲 Misaki

私は行こうと思ってるよ。
Watashi wa ikō to omotteru yo.
I'm thinking of going.

Sources

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