Present but only just perceptible. Subtlety is doing the work without announcing it.
Latin subtilis (finely woven, delicate), from sub (under) + tela (a web, a loom's warp), from texere (to weave); the finest thread in a weave is the one that does the work without being seen doing it.
Present, but only just perceptible. Subtlety does the work without announcing it, exactly as the finest thread in a weave is never the one anyone notices.