subtle
adj//ˈsʌtl̩//subtil
Of an argument or concept, words, etc.: requiring one to distinguish between fine points, especially if it is difficult to do so; nice; also (generally) , difficult to grasp; not easily understood or obvious.
(archaic) Of a person or animal, or of an action or words: clever or skilful in a crafty or devious way; cunning, sly, wily.