So slight as to be difficult to detect or describe; elusive, Operating in a hidden, usually injurious way; insidious, Characterized by refinement and niceness in drawing distinctions; nicely discriminating; -- said of persons; ; refined; tenuous; sinuous; insinuating; hence, penetrative or pervasive; -- said of the mind; its faculties, or its operations; ; also, difficult of apprehension; elusive

marked by richness and fullness of flavor, Sensible (of intellect etc.); straightforward, not given to or confused by uncertainty or subtlety, Evincing strength; indicating vigorous health; strong; sinewy; muscular; vigorous; sound; as, a robust body; robust youth; robust health

To reduce to a pure state; purify, To use precise distinctions and subtlety in thought or speech, To improve in accuracy, delicacy, or excellence, transitive verb_ To reduce to a fine, unmixed, or pure state; to free from impurities; to free from dross or alloy; to separate from extraneous matter; to purify; to defecate, To purify from what is gross, coarse, vulgar, inelegant, low, and the like; to make elegant or exellent; to polish, verb_ To reduce to a fine, unmixed, or pure state; to free from impurities; to free from dross or alloy; to separate from extraneous matter; to purify; as, to refine gold or silver; to refine iron; to refine wine or sugar, To become pure; to be cleared of feculent matter, To affect nicety or subtlety in thought or language

easily perceived by the senses or grasped by the mind, Easily discovered, seen, or understood; self-explanatory, Easily seen through because of a lack of subtlety; transparent