Definitions of subtle on the Web:
elusive: be difficult to detect or grasp by the mind; “his whole attitude had undergone a subtle change”; “a subtle difference”; “that elusive thing the soul”
faint and difficult to analyze; “subtle aromas”
able to make fine distinctions; “a subtle mind”
insidious: working or spreading in a hidden and usually injurious way; “glaucoma is an insidious disease”; “a subtle poison”
wordnet.princeton.edu/perl/webwn
Complex and balanced; implies more participating elements than “delicate,” but balance is critical. A wine that’s “outrageous” or “in-your-face” may be complex, but it isn’t likely to be subtle.
http://www.st-kathryn-cellars.com/glossary.htm
A positive characteristic usually referring to a delicate wine that offers up nuances of flavor and aroma.
http://www.valleyvineyards.com/wine_glossary_stuv.htm
The elements of interest are not obvious on the palate. Contrast with “big”.
http://www.mcgees.org/popupmaltglossary.html
Delicate wines with finesse and elegance. Understated flavors that are well integrated and inspiring.
http://www.grape-nutz.com/tastings/glossary.html
well you did ask………. 😉