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

1) To make less dense.
2) To become less dense; become thinned.
Related concepts: → attenuate, → dilute, → decompress.

M.E. rarefien, from M.Fr. rarefier, from rare, combining form of rarus "loose, wide apart, thin, infrequent."

Alaridan, infinitive of âlar, from intensive/nuance prefix â- + lar "thin, meagre" (Dehxodâ), Lori, Laki larr, larrek "thin cow or sheep," Kurd. lerr "thin, lean," variants of laqar (Torbat-Heydariyé), lâqar "lean, meagre, slender; weak."