| Word | Definition |
|---|---|
| xenobiologist n. (1954) | one who studies xenobiology |
| xenobiology n. (1954) | the study of the biology of extraterrestrial life forms |
| xenocidal adj. (1979) | of, pertaining to, or involving xenocide n. |
| xenocide n. (1973) | the killing or attempted killing of an entire alien species; the killing of an individual alien; (also) a person who commits this act |
| xenolinguist n. (1955) | one who studies alien languages |
| xenological adj. (1950) | of, or relating to, xenology |
| xenologist n. (1949) | one who studies xenology n. |
| xenology n. (1954) | the scientific study of aliens, esp. xenobiology n. |
| X-Phile n. (1994) | a fan of the TV show The X-Files |
| zap gun n. (1934) | = ray gun n. |
| zero-g n. (1940) | = zero-gravity n. |
| zero-gravity n. (1938) | the state or condition in which there is no apparent force of gravity acting on a body, either because the force is locally weak, or because both the body and its surroundings are freely and equally accelerating under the force |
| zine n. (1944) | = fanzine n. |