WordNet sense 1 (an informal form of address for a man):

buster, dude

WordNet sense 2 (a person who is frequently in the company of another):

associate, companion, comrade, familiar, associate

WordNet sense 3 (a person who is member of your class or profession):

colleague, confrere

WordNet sense 4 (a boy or man):

chap, cuss, gent, lad, blighter, fella, feller

WordNet sense 5 (a man who is the lover of a girl or young woman):

beau, boyfriend, swain, young man