without studying; not having studied
Slang noun used mainly by students to describe taking a test or exam without any preparation. Often used in phrases like 無勉で受ける (take without studying).
I have no choice but to take tomorrow's test without studying.
I didn't study, but I did surprisingly well.
Abbreviation of 無勉強 (むべんきょう), literally 'no study'. The exact origin is uncertain, but it likely arose as student slang.