Sly in design; artful; cunning; insinuating; subtile; -- applied to persons; as, a subtle foe.
- So slight as to be difficult to detect or describe; elusive: a subtle smile.
- Difficult to understand; abstruse: an argument whose subtle point was lost on her opponent.
- Able to make fine distinctions: a subtle mind.
- Characterized by skill or ingenuity; clever.
- Crafty or sly; devious.
- Operating in a hidden, usually injurious way; insidious: a subtle poison.