/ ˈfliːtɪŋ; NAmE / adjective
[ usually before noun ] lasting only a short time
SYN brief :
a fleeting glimpse / smile
a fleeting moment of happiness
We paid a fleeting visit to Paris.
► fleet·ing·ly adverb
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WORD ORIGIN
Old English (in the sense floating, swimming ): from fleet move or pass quickly + -ing .