Subtle, a. [Compar. Subtler; superl. Subtlest.]
Etymology: [OE. sotil, subtil, OF. soutil, later subtil, F. subtil, L. subtilis; probably, originally, woven fine, and fr. sub under + tela a web, fr. texere to weave. See Text, and cf. Subtile.]
1. Sly in design; artful; cunning; insinuating; subtile; -- applied to persons; as, a subtle foe. "A subtle traitor." Shak.
2. Cunningly devised; crafty; treacherous; as, a subtle stratagem.
3. 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. Things remote from use, obscure and subtle. Milton.
4. Smooth and deceptive. [Obs.] Like to a bowl upon a subtle ground [bowling ground]. Shak.
1 more senses
Syn. -- Artful; crafty; cunning; shrewd; sly; wily. Subtle is the most comprehensive of these epithets and implies the finest intellectual quality. See Shrewd, and Cunning.
Shades of meaning
Fernald has no entry of its own for subtle; he lists it under astute, fine.
He lists it without comment; the entries above explain its neighbors.