Fleeting is an adjective that refers to something that lasts for a very short period of time. Some synonyms for the word fleeting include transient, brief, momentary, evanescent, passing, temporary, ephemeral, fading, impermanent, and short-lived. These synonyms can be used interchangeably depending on the context in which they are used. For instance, if you want to describe a memory that only lasts for a short duration, you can use the words fleeting, transient, or momentary. Other synonyms like passing or ephemeral can be used to describe things that vanish quickly or are of short duration. Overall, understanding synonyms of the word fleeting can help to spice up one's writing.