Having difficulty breathing; gasping. / That makes one hold one's breath (with excitement etc.). / Not breathing; dead or apparently so. / Having no wind; still, calm or airless.

The state of being breathless or out of breath. / (pathology) Difficult or labored respiration, dyspnea, shortness of breath

plural of breathlessness

In a breathless manner, usually due to excitement, exertion, etc.