1. an earphone that is inserted into the ear canal;
2. a plug of cotton, wax, or rubber that is fitted into the ear canal for protection against the entry of water or loud noise;
WordNet (r) 3.0 (2006):
earplug
n 1: an earphone that is inserted into the ear canal
2: a plug of cotton, wax, or rubber that is fitted into the ear
canal for protection against the entry of water or loud noise