na-adjective, noun
malicious; spiteful; underhanded
Describes a person, behavior, or atmosphere that is mean-spirited in a sneaky, indirect way. Often used for bullying, harassment, or a gloomy, oppressive mood.
彼の陰湿ないじめに耐えられなかった。
I couldn't stand his underhanded bullying.
職場の陰湿な雰囲気が嫌だ。
I hate the malicious atmosphere at work.
na-adjective, noun
shady and damp
Literal, physical sense: a place that is dark, humid, and unpleasant. Less common than the figurative sense.
この地下室は陰湿でカビ臭い。
This basement is shady, damp, and smells of mold.
Compound of 陰 (shade, dark, hidden) and 湿 (damp, moist). The figurative sense of 'malicious' derives from the unpleasant, oppressive feeling associated with dark, damp places.