transient (adj.)

c. 1600, "transitory, passing with time, not durable," from Latin transientem (nominative transiens) "passing over or away," present participle of transire "cross over, go over, pass over, hasten over, pass away," from trans "across, beyond" (see trans-) + ire "to go" (from PIE root *ei- "to go").

Strictly, transient marks the fact that a thing soon passes or will soon pass away ; as, a transient impression : a transient shadow. Transitory indicates that lack of permanence is in the nature of the thing: as, transitory pleasure ; this transitory life. [Century Dictionary]

By 1610s as "passing across," as from person to person or place to place. The meaning "passing through a place without staying" is from 1680s.

The noun is attested by 1650s, "transient thing or being;" specific sense of "transient guest or boarder, person who passes through a place and stays only a short time" is attested by 1857. Related: Transiently.