also: ずい
na-adjective, noun
voluntary; optional; at one's discretion
Describes something done by free choice, without compulsion. Common in formal contexts such as rules, contracts, and official notices.
参加は随意ですので、ご都合に合わせてお越しください。
Participation is voluntary, so please come at your convenience.
この書類の提出は随意とされています。
Submission of this document is considered optional.
Irregular kana usage. Rarely encountered.
任意 is more common in everyday and legal contexts for 'optional' or 'arbitrary'. 随意 is more formal and often used in official or written language.
自由 means 'free' in a broad sense of freedom or liberty. 随意 specifically refers to the absence of obligation or the freedom to choose in a particular matter.
Compound of 随 (follow, comply) and 意 (mind, intention), literally 'following one's intention'. The meaning 'voluntary' or 'at one's discretion' is a natural extension.