Spermaceti / spɜːməˈsiːti / is a waxy substance found in the head cavities of the sperm whale (and, in smaller quantities, in the oils of other whales). Spermaceti is created in the spermaceti organ inside the whale's head. This organ may contain as much as 1,900 litres (500 US gal) of spermaceti.

spermaceti, a wax, liquid at body temperature, obtained from the head of a sperm whale or bottlenose whale. Spermaceti was used chiefly in ointments, cosmetic creams, fine wax candles, pomades, and textile finishing; later it was used for industrial lubricants.

The spermaceti organ is an organ present in the heads of toothed whales of the family Physeteroidea, in particular the sperm whale. This organ contains a waxy liquid called spermaceti and is involved in the generation of sound.