【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.