noun
Used in medical, biological, or formal contexts to describe actions or movements that occur without conscious control, such as reflexes or autonomic functions. Often contrasted with 随意 (voluntary).
不随意運動は、自分の意思とは関係なく起こる。
Involuntary movements occur regardless of one's will.
心臓の拍動は不随意の働きだ。
The heartbeat is an involuntary function.
Formed from 不 (negative prefix) + 随意 (voluntary, at will). The word is a Sino-Japanese compound used primarily in technical and medical vocabulary.