pl. n. xenomorphs; adj. xenomorphic; also xeno, xenos
1. n., (“zee’ no morf”) in fandom, the name for the endoparasitoid extraterrestrial species featured as the main antagonists in the Alien franchise; the term itself was first used in canon in 1986’s Aliens; from Greek xenos “foreign, strange” + morphē “form, shape.” See alien.
2. in science fiction film, literature and gaming milieux, syn. of alien; often shortened to “xeno.”
3. xeno, in Games Workshop’s Warhammer 40,000 science-fiction wargaming and role-playing milieu, any of a number of alien, non-human races, esp. the Tyranids, which are inspired by the Alien xenomorphs.
Addendum: Also, in geology, “xenomorph” is a syn. of “allotriomorph,” “a mineral that did not develop its otherwise typical external crystal form because of late crystallization between earlier formed crystals, typical of matrix minerals in rapidly crystallizing volcanic lavas and shallow igneous intrusions.” So there’s that. Source.