Source : Webster's Revised Unabridged Dictionary (1913)

Respirator \Res"pi*ra`tor\ (r?s"p?*r?`t?r), n. [Cf. F.
   respirateur.]
   A divice of gauze or wire, covering the mouth or nose, to
   prevent the inhalation of noxious substances, as dust or
   smoke. Being warmed by the breath, it tempers cold air
   passing through it, and may also be used for the inhalation
   of medicated vapors.

Source : WordNet®

respirator
     n 1: a breathing device for administering long-term artificial
          respiration [syn: {inhalator}]
     2: a protective mask with a filter; protects the face and lungs
        against poisonous gases [syn: {gasmask}, {gas helmet}]