ephemeron

noun
1

Something short-lived or transitory.

2

A type of weak reference in a garbage collected programming language that does not permit an object to be kept alive by its finalizer.

Source: https://en.wiktionary.org/wiki/ephemeron

Definitions come from the Free Dictionary API (dictionaryapi.dev), with Wiktionary as a fallback when it is slow, and are cached for up to 24 hours.