Desalt is from de- ('removal') + salt, the latter from Old English sealt, from Proto-Germanic *saltą, from Proto-Indo-European *séh₂ls ('salt'). The ancestry passes through Latin de-, Old English sealt, and Proto-Indo-European *séh₂ls. The prefix de- often marks removal, reversal, or downward motion in Latin formations, helping to explain the word's surface structure. In present use as a verb, it means "to remove salt from, especially from seawater", keeping the historical formation close to the word's ordinary semantic work. Related words include salt, desalination, and salinity; derived forms include desalting and desalted.