Subtle

Webster's Dictionary of the English Language

·superl Smooth and deceptive.

II. Subtle ·superl Cunningly devised; crafty; treacherous; as, a subtle stratagem.

III. Subtle ·superl Sly in design; artful; cunning; insinuating; subtile;

— applied to persons; as, a subtle foe.

IV. Subtle ·superl Characterized by refinement and niceness in drawing distinctions; nicely discriminating;

— said of persons; as, a subtle logician; refined; tenuous; sinuous; insinuating; hence, penetrative or pervasive;

— said of the mind; its faculties, or its operations; as, a subtle intellect; a subtle imagination; a subtle process of thought; also, difficult of apprehension; elusive.