The word “subtle” can have different meanings. In its broadest sense, subtle means something that isn’t obvious and is difficult to detect. e.g. A subtle smile came across her face. Her attitude toward him had undergone a subtle change. Other meanings of subtle include being skillful, perceptive, and having the ability to make fine distinctions. Subtle can also refer to something that works insidiously (such as a drug or poison). However, these meanings aren’t used all that often (that is compared to the first meaning I gave).

subtle adjective approving • not loud, bright, noticeable or obvious in any way The room was painted a subtle shade of pink. The play's message is perhaps too subtle to be understood by young children. • small but important There is a subtle difference between these two plans. • achieved in a quiet way which does not attract attention to itself and which is therefore good or clever a subtle plan/suggestion subtle questions http://www.visualthesaurus.com/landing/?ad=cdo&utm_medium=default&utm_campaign=VT&utm_source=cdo&word=subtle

It means a 1. little, delicate, or 2. skillful, clever But we really only use it as 1

not overt

not pronounced, protrusive, prominent--only faintly/finely/finitely traceable/detectable (wine tasting, tea imbibing)