coxcomb \KOKS-kohm\ (noun) - 1 : obsolete. A cap worn by court jesters; adorned with a strip of red. (Now cockscomb). 2 : archaic. The top of the head, or the head itself. 3 : Obsolete. A fool. 4 : A vain, showy fellow; a conceited, silly man, fond of display; a superficial pretender to knowledge or accomplishments; a dandy; a fop.
"Not at all -- I never saw him; but I fancy he is very unlike his brother -- silly and a great coxcomb." -- Jane Austen, 'Sense and Sensibility'
Coxcomb is a corrupted spelling of cock's comb, the comb of a rooster, hence the badge resembling it that was worn in the cap of a professional fool or jester, hence the wearer of the cap, hence a fool or a vain and silly man.