any of a family (Physeteridae) of toothed whales; esp., a large species (Physeter catodon) inhabiting warm seas: a closed cavity in its roughly square head contains sperm oil
- A very large toothed whale (Physeter macrocephalus syn. P. catodon) formerly hunted for the spermaceti in its massive head and the ambergris in its intestines. Also called cachalot.
- Either of two small toothed whales (Kogia breviceps or K. sima) also containing spermaceti in the head.