late 14c., "acuteness, skill, cunning," alteration of subtlety (q.v.) on model of subtile, or else from Old French subtilite, from Latin subtilitas "fineness, simplicity."
Entries linking to subtility
subtlety n.
c. 1300, sotilte, "skill, ingenuity," from Old French sotilte "skillfulness, cunning" (Modern French subtilité), from Latin subtilitatem (nominative subtilitas) "fineness; simplicity, slenderness," noun of quality from subtilis "fine, thin, delicate" (see subtle). From late 14c. as "cleverness, shrewdness; trickery, guile, craftiness," also "thinness, slenderness, smallness; rarity." The -b- begins to appear late 14c. in English, in imitation of Latin.
subtile adj.
c. 1300, sotil; modern form from late 14c., "clever, dexterous, crafty; not dense, thin, rarefied," from Old French subtil (14c.), a learned Latinized reformation of earlier sotil (12c.), source of subtle (q.v.). Still used in some Bible translations in Genesis iii.1, and it survived after 17c. as a parallel formation to subtle in some material senses ("fine, delicate, thin"). Related: Subtilly.