Definition of "ephemeron"

Ah!—so frail are we—So like the brief ephemeron that wheelsIts momentary round, we scarce can weepOur own bereavements, ere we haste to shareThe clay with those we mourn.

1834, Lydia Sigourney, Poems, To the Memeory of a Young Lady, page 64

Beyond type safety, OCaml has several features that closely interact with the garbage collector. These include weak references, finalisers, ephemerons, and lazy values, whose semantics will have to be preserved with the new GC so as to not break programs that use those features.

2020, KC Sivaramakrishnan et al., Retrofitting Parallelism onto OCaml‎