The Collaborative International Dictionary of English v.0.48:

Suspender \Sus*pend"er\, n.
   One who, or that which, suspends; esp., one of a pair of
   straps or braces worn over the shoulders, for holding up the
   trousers.
   [1913 Webster]

WordNet (r) 3.0 (2006):

suspender
    n 1: elastic straps that hold trousers up (usually used in the
         plural) [syn: brace, suspender, gallus]