expression, noun
unconcerned air; nonchalant manner; acting as if nothing happened
A rare, literary set phrase describing a person's demeanor when they pretend nothing is wrong or act casually to hide their true feelings. Often used in narrative or classical contexts.
彼はさあらぬ体で部屋を出て行った。
He left the room with an unconcerned air.
さあらぬ体を装って、彼女は秘密を守った。
She kept the secret by putting on a nonchalant manner.
Derived from classical Japanese 然有らぬ (sa aranu, 'not being so') + 体 (tei, 'appearance'). The exact historical development is uncertain, but it is a fossilized literary expression.