An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The state of being rarefied, less dense.
An instantaneous reduction in density of a gas resulting from passage a sound wave; opposite of → compression.

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.

A pressure wave in a fluid generated by rarefaction. It travels in the opposite direction to that of a shock wave in the medium.

→ rarefaction; → wave.