Transient, transitory, passing, ephemeral, momentary, fugitive, fleeting, evanescent, short-lived are comparable when they mean lasting or staying only for a short time.
Transient and transitory are often used as if they were interchangeable; but transient more frequently applies to what is actually short in its duration or stay and transitory , like its close synonym passing , to what is by its nature or essence bound to change, pass, or come to an end sooner or later.
Ephemeral may imply existence for only a day. In extended use, it implies marked shortness of life or of duration (as of influence or appeal).
Momentary implies duration for a moment or a similar very short time.
Fugitive and fleeting apply to what passes swiftly, and is gone; but fugitive carries a stronger implication of the difficulty of catching or fixing and fleeting , of the impossibility of holding back or restraining from flight.
Evanescent implies momentariness, but it stresses quick and complete vanishing, and it usually connotes a delicate, fragile, or airy quality.
Short-lived implies extreme brevity of life or existence often of what might be expected to last or live longer.