rarefy
v.
late 14c., from Old French rarefier (14c.) and directly from Medieval Latin rarificare, from Latin rarefacere "make rare," from rarus "rare, thin" (see rare, adj.1) + facere "to make" (see factitious). Related: Rarefied.
〔李〕[rare a. 稀薄的；-fy ⇒“to make rare使稀薄”→] vt. make less dense使稀薄，使稀少