cet(o)-

A whale.

Latin cetus, from Greek ketos, whale or sea-monster.

A cetacean is a member of an order of marine mammals that comprises the whales, dolphins, and porpoises; cetology is the branch of zoology dealing with whales and dolphins. Cetane is a hydrocarbon present in petroleum spirit, so named because related compounds were first derived from spermaceti, often used as a standard against which to measure the ignition properties of diesel fuel.