also: とんちゃくない
i-adjective
indifferent; unconcerned; not caring
Describes a person who does not worry about or pay attention to something, often used in the negative form 頓着しない. The adjective 頓着ない is somewhat literary.
彼は他人の評価に頓着ない。
He is indifferent to other people's opinions.
彼女は服装に頓着しない。
She doesn't care about her clothes.
From 頓着 (とんじゃく, 'caring, worrying') + ない (negative). 頓着 is a Sino-Japanese word (kango) meaning 'to be concerned about'. The exact derivation of 頓着 is uncertain, but it is conventionally associated with the kanji 頓 (sudden, immediate) and 着 (arrive, wear).