a. Thin; not dense or gross; rare; as, subtile air; subtile vapor; a subtile medium. a. Delicately constituted or constructed; nice; fine; delicate; tenuous; finely woven. a. Acute; piercing; searching. a. Characterized by nicety of discrimination; discerning; delicate; refined; subtle. a. Sly; artful; cunning; crafty; subtle; as, a subtile person; a subtile adversary; a subtile scheme.