expression
have no idea; have no clue; can't think of anything
Used when you cannot recall or think of any relevant information, person, or possibility. Often appears in negative form 心当たりがない. The related phrase 心当たりのない is an adnominal form.
See also: 心当たりのない
Antonyms: 心当たりがある
誰がそんなことをしたのか、まったく心当たりがない。
I have absolutely no idea who did such a thing.
彼女が怒っている理由に心当たりがない。
I have no clue why she is angry.
Compound of 心 (こころ, 'mind') + 当たり (あたり, 'hitting upon') + が + ない ('not'). Literally 'there is no hitting upon in the mind', i.e., nothing comes to mind.