WordWeb Online

1. Not breathing or able to breathe except with difficulty
   "breathless at the thought of what I had done"; "followed the match with breathless interest";
   - dyspneic [Brit, N. Amer], dyspnoeic [Brit, Cdn], dyspneal [N. Amer], dyspnoeal [Brit, Cdn], dyspoeic, dyspeic
    
2. Tending to cause suspension of regular breathing
   "a breathless flight"
    
3. Appearing dead; not breathing or having no perceptible pulse
   - inanimate, pulseless
    
4. Breathing heavily (as after exertion)
   - out of breath, puffed [Brit], gasping, short-winded

See also: asphyxiating, blown, choking, dead, exciting, pursy [archaic], short-winded, smothering, suffocating, suffocative, unventilated, winded

Encyclopedia: Breathless