| Word | Definition |
|---|---|
| trivee n. (No cites) | see tri-v n. |
| tri-vid n. (1955) | a device or system capable of transmitting or displaying a three-dimensional image |
| trufan n. (1954) | a science fiction fan who adheres to the ideals and practices of fandom |
| trufandom n. (1954) | the state of being a trufan; excellence in fannish behavior |
| uchronia n. (1976) | = alternate history n. |
| uchronian adj. (1986) | of uchronias |
| uchronic adj. (1991) | of uchronias |
| UFO n. (1953) | an unidentified flying object; a βflying saucerβ |
| ultradrive n. (1951) | a type of faster-than-light star drive |
| ultraphone n. (1928) | a communications device that transmits messages faster than the speed of light |
| ultrawave n. (1934) | a communication system that transmits messages faster than the speed of light; (also) a wave phenomenon used by such devices |
| unfannish adj. (1958) | failing to be fannish; not having the attributes of a dedicated or obsessive fan |
| unhuman n. (1944) | an intelligent nonhuman entity; alien n.; cf. non-human n. |
| universe n. (1947) | the setting of a work or series of fiction, esp. of imaginative fiction |
| unobtainium n. (1956) | a hypothetical substance that would be highly desirable but is unrealized or unobtainable; a notional substance with exceptional or ideal properties |
| unperson n. (1949) | a person who, usually for political reasons, is deemed not to have existed and whose name is removed from all public records; hence, more generally: a person whose contributions or achievements are officially denied or disregarded; a person regarded as less than human |
| unsuit v. (1957) | to remove a spacesuit |
| unsuited adv. (1957) | without wearing a spacesuit |
| uplift n. (1980) | the making of a sentient species from a non-sentient one, esp. by genetic engineering |
| uplift v. (1980) | to transform a non-sentient species into a sentient species, esp. by genetic engineering |
| uplifter n. (2006) | a genetic engineer who carries out uplift n. |
| uplifting n. (1980) | = uplift n. |
| uptime adj. (1978) | esp. in time-travel contexts: in or from the future; cf. downtime adj. |
| uptime adv. (1972) | esp. in time-travel contexts: in, into, or toward the future; cf. downtime adv. |
| Uranian n. (1834) | a native or inhabitant of Uranus |
| urban fantasy n. (1978) | a genre of fantasy that uses a city as its primary setting; a work in this genre |
| utopia n. (No cites) | a place, state, or condition ideally perfect in respect of politics, laws, customs, and conditions |
| utopian n. (No cites) | one who conceives, proposes, or introduces schemes supposed or intended to bring about improved or perfect social and political conditions, etc.; an advocate of social reform |
| utopian adj. (1981) | possessing or regarded as having impossibly or extravagantly ideal conditions in respect of politics, customs, social organization, etc. |
| utopic adj. (No cites) | that embodies or proposes utopian ideals |
| vacsuit n. (1942) | = vacuum suit n. |
| vacsuited adj. (1993) | = vacuum-suited adj. |
| vacuum suit n. (1926) | = space suit n. |
| vacuum-suited adj. (1947) | wearing a vacuum suit n. |
| vape v. (1983) | to vaporize by means of a weapon; to destroy completely, annihilate |
| Vegan n. (1932) | a native or inhabitant of the solar system of the star Vega |
| Vegan adj. (1940) | of or pertaining to the star Vega, or the natives or inhabitants of its solar system |