also: むとんじゃく
na-adjective, noun
indifferent; unconcerned; nonchalant
Describes a lack of interest or worry about something, often with a nuance of not caring enough. Used for people's attitudes toward appearance, rules, details, or others' opinions.
彼は服装に無頓着だ。
He is indifferent to his clothes.
彼女は他人の評
She has a side that is unconcerned with others' opinions.
Compound of 無 (without) and 頓着 (concern, worry). 頓着 itself is a Sino-Japanese word meaning to be preoccupied or concerned.