Fleeting means something that lasts for a very short time, quickly passing or appearing and then disappearing. It can also refer to something that is transient or temporary in nature.
Usage examples
The feeling of happiness was only fleeting, as it disappeared as quickly as it came.
As I looked out the window, I caught a fleeting glimpse of a beautiful rainbow.
He only had a fleeting moment to make a decision before the opportunity passed.
The butterfly's visit to the garden was fleeting; it fluttered away in a matter of seconds.
The thought of going on vacation brought a fleeting smile to her face before she returned to her work.
Together, this broken family is at once specific to their surroundings and, in fleeting moments of gorgeous honesty, universal. (backstage.com)
The murals here, seemingly simplistic, address pop culture as well as issues of race, class and the fragmented, fleeting nature of memory. (latimes.com)
More often than not, camera traps yield only fleeting glimpses of target species passing by the lens, leaving researchers with perhaps two or three clear frames with which to study. (treehugger.com)