unhappenable

From un- +‎ happen +‎ -able.

unhappenable (comparative more unhappenable, superlative most unhappenable)

1. (rare, often humorous) Not happenable; synonym of impossible.
   • 1925, Willard Johnson, “The good old days: (Santa Fe: with foot-notes).”, in Southwest Review, volume 10, number 4, →JSTOR, pages 66–72:

     A lawyer who came to the village only fifteen or so years ago assures me that the things which occurred during his first few seasons here are absolutely unhappenable now.

   • 1967, Austin Clarke, “More Extracts from a Diary of Dreams”, in Old-Fashioned Pilgrimage and Other Poems, Dolmen Press, →ISBN:

     Why should the aged be unhappy, / Mope in the dark, when the unhappenable / Is theirs and they can glide between the shades / Of meaning in a dream, talk to the shades […]

   • 2007, Rabbis of Boca Raton Theological Seminary, How to Raise a Jewish Dog‎^[1], Little, Brown, →ISBN:

     Then you'll be ready if the unthinkable happens. Just because it's unthinkable doesn't mean it's unhappenable.

• unpossible

• happenable