The Collaborative International Dictionary of English v.0.48:

rubber band \rub"ber band"\, n.
   A closed loop of rubber usually having a thin rectangular
   cross-section; also called elastic band; -- it varies in
   length from the circumference of a finger to several inches,
   and is usually used to hold several objects together
   temporarily, by the tension exerted when the band is
   stretched and fitted around the objects to be held; as, to
   hold a pack of cards together with a rubber band.
   [PJC]

WordNet (r) 3.0 (2006):

rubber band
    n 1: a narrow band of elastic rubber used to hold things (such
         as papers) together [syn: rubber band, elastic band,
         elastic]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "rubber band":
   Lastex, baleen, battledore, chewing gum, elastic, elastomer, gum,
   gum elastic, handball, jumping jack, racket, rubber, rubber ball,
   spandex, spring, springboard, stretch fabric, trampoline,
   whalebone