WordNet (r) 3.0 (2006):

headset
    n 1: receiver consisting of a pair of headphones

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "headset":
   acoustical network, capacitor speaker, coaxial speaker, cone,
   crossover network, diaphragm, dynamic speaker, earphone,
   electrodynamic speaker, electromagnetic speaker,
   electrostatic speaker, excited-field speaker,
   full-fidelity speaker, headphone, high-fidelity speaker,
   high-frequency speaker, horn, loudspeaker, low-frequency speaker,
   midrange speaker, monorange speaker, moving-coil speaker,
   permanent magnet speaker, radiophone, radiotelephone, speaker,
   speaker system, speaker unit, triaxial speaker, tweeter,
   voice coil, wireless, wireless telephone, woofer