1.a boy or man;
that chap is your host
2.a person who is frequently in the company of another;
drinking companions
3.a person who is member of your class or profession;
the surgeon consulted his colleagues
4.an informal form of address for a man;
Say, fellow, what are you doing?
5.a man who is the lover of a girl or young woman;
if I'd known he was her boyfriend I wouldn't have asked