noun which may take the genitive case particle 'no', na-adjective, noun, noun, used as a suffix
wrong; bad; improper; inadvisable
Used to describe something that is morally or practically unacceptable, not right, or not advisable. Often appears in formal or written contexts.
そのような行為は不可だ。
Such behavior is unacceptable.
この計画は予算的に不可と判断された。
This plan was judged infeasible from a budgetary standpoint.
noun which may take the genitive case particle 'no', na-adjective, noun, noun, used as a suffix
Indicates prohibition or impossibility. Common in rules, signs, and formal statements. Also used as a suffix (〜不可) meaning 'cannot be done' or 'not permitted'.
ここでの写真撮影は不可です。
Photography is not allowed here.
この書類は再発行不可となっております。
This document cannot be reissued.
noun
Specifically refers to a failing mark in an academic or evaluative context. Often contrasted with 可 (pass).
期末試験で不可を取ってしまった。
I got a failing grade on the final exam.
駄目 is a more casual and versatile word for 'no good' or 'not allowed', whereas 不可 is more formal and often written.
Compound of 不 (fu, 'not') and 可 (ka, 'permissible' or 'possible'). The kanji combination directly yields the meaning 'not permissible/possible'.