*subtle*:
Adjective
Inflected forms: sub·tler, sub·tlest 1. a. So slight as to be difficult to detect or describe; elusive: a subtle smile. b. Difficult to understand; abstruse: an argument whose subtle point was lost on her opponent. 2. Able to make fine distinctions: a subtle mind. 3. a. Characterized by skill or ingenuity; clever. b. Crafty or sly; devious. c. Operating in a hidden, usually injurious way; insidious: a subtle poison.