1. (physics) the mass of a body in motion relative to the observer: it is equal to the rest mass multiplied by a factor that is greater than 1 and that increases as the magnitude of the velocity increases;
WordNet (r) 3.0 (2006):
relativistic mass
n 1: (physics) the mass of a body in motion relative to the
observer: it is equal to the rest mass multiplied by a
factor that is greater than 1 and that increases as the
magnitude of the velocity increases