The state of being rarefied, less dense.
M.E. rarefien, from M.Fr. rarefier, from L. rarefacere "make rare," from rarus "loose, wide apart, thin, infrequent."
Verbal noun from âlar present stem of âlaridan→ rarefy + -š, a suffix.
Fr.: onde de raréfaction
A pressure wave in a fluid generated by rarefaction. It travels in the opposite direction to that of a shock wave in the medium.