1. (a.) Thin; not dense or gross; rare; as, subtle air; subtle vapor; a subtle medium.

2. (a.) Delicately constituted or constructed; nice; fine; delicate; tenuous; finely woven.

3. (a.) Acute; piercing; searching.

4. (a.) Characterized by nicety of discrimination; discerning; delicate; refined; subtle.

5. (a.) Sly; artful; cunning; crafty; subtle; as, a subtle person; a subtle adversary; a subtle scheme.

Byzantine Machiavellian Machiavellic acute adulterated air-built airy arch artful astute attenuate attenuated cagey calculating canny chimerical clever cloud-built crafty cunning cut cute dainty deceitful deep deep-laid delicate designing devious dilute diluted diplomatic dreamlike ethereal fanciful fatuitous fatuous feline fine flimsy foxy gaseous gossamery guileful illusory imaginary ingenious insidious insubstantial inventive knowing pawky phantomlike politic rare rarefied ready resourceful scheming serpentine shadowy sharp shifty shrewd slick slight slippery sly smooth snaky sneaky sophistical spirituous stealthy strategic subtle supple tactical tenuous thin thinned thinned-out trickish tricksy tricky uncompact uncompressed unreal unsubstantial vaporous vulpine wary watered watered-down wily windy