(n.) The distinguishing part or essence of a species; the characteristic attribute of a species\; specific difference.

atmosphere attribute aura badge balm balminess bouquet brand breath cachet cast character characteristic configuration cut definite odor detectable odor differentia differential distinctive feature earmark effluvium emanation essence exhalation feature fetor figure flavor fragrance fragrancy fruitiness fume gust hallmark hint idiocrasy idiosyncrasy impress impression incense index individualism keynote lineaments mannerism mark marking mephitis mold muskiness nature nosegay odor particularity peculiarity perfume property quality quirk redolence reek savor scent seal shape singularity smack smell specialty spice spiciness spoor stamp stench stink subtle odor suggestion sweet savor sweet smell taint tang taste token trace trail trait trick whiff