transient

one who stays for only a short time; "transient laborers"

(physics) a short-lived oscillation in a system caused by a sudden change of voltage or current or load

of a mental act; causing effects outside the mind

lasting a very short time; "the ephemeral joys of childhood"; "a passing fancy"; "youth's transient beauty"; "love is transitory but it is eternal"; "fugacious blossoms"