groomsman

from WordNet (r) 3.0 (2006)

groomsman
    n 1: a male attendant of the bridegroom at a wedding

from The Collaborative International Dictionary of English v.0.48

Groomsman \Grooms"man\, n.; pl. {Groomsmen}.
   A male attendant of a bridegroom at his wedding; -- the chief
   attendant is also called the {best man}; -- the correlative
   of {bridesmaid}.
   [1913 Webster]