From Greek ketos over Latin cetus to the whale-contexting prefix

The Greek word ketos and the Latin noun cetos, derived therefrom, mean whale or sea-monster [1]. Various scientific terms, in use today, stem linguistically from these roots. Cetology refers to the branch of zoology that studies whales and dolphins. They are not considered sea-monster any more. In scientific classification, the term Cetacea denotes the order of marine mammals that includes the suborders Mysticeti (ballen whales) and Odontoceti (toothed whales).

In chemistry, the alkane compound hexadecane (C₁₆H₃₄) is also called cetane since some of its derivatives were first found in whale oil. The prefix cetyl is synonymously used for hexadecyl, CH₃(CH₂)₁₅-, to specify a group or substituent with this constitution. The best known compound, carrying this prefix in its name, probably is cetyl alcohol, CH₃(CH₂)₁₅OH, which is also named palmityl alcohol and 1-hexadecanol. The occurrence of the cetyl prefix in a chemical substance name characterizes a compound structurally, but does not relate to the “cetobiochemistry” of the compound.

Reference
[1] Michael Quinion: OLOGIES AND ISMS • Word Beginnings and Endings. Oxford University Press, Oxford and New York, 2002.