1836, from Cetacea, name of the order of marine mammals, + -an. As an adjective, "pertaining to the whale," from 1839.
Entries linking to cetacean
Cetacea n.
order of marine mammals including whales, 1795, Modern Latin, from Latin cetus "any large sea creature" (whales, seals, dolphins), from Greek kētos "a whale, a sea monster," which is of unknown origin, + -acea.
-an
word-forming element meaning "pertaining to," from Latin -anus, adjective suffix, in some cases via French -ain, -en. From PIE *-no-.