subtlety
sub.tle.ty \'s*t-*l-te-\ n [ME sutilte, fr. OF sutilte`, fr. L subtilitat-, subtilit]as, fr. subtilis 1: the quality or state of being subtle : as 1a: TENUOUSNESS 1b: acuteness of mind 2: something subtle; esp : a fine distinction
Webster's English Dictionarysub.tle.ty \'s*t-*l-te-\ n [ME sutilte, fr. OF sutilte`, fr. L subtilitat-, subtilit]as, fr. subtilis 1: the quality or state of being subtle : as 1a: TENUOUSNESS 1b: acuteness of mind 2: something subtle; esp : a fine distinction