undoing

Etymology 1

From Middle English undoinge, undoynge, ondoynge; equivalent to undo + -ing.

noun

1. The act of loosening or unfastening
2. Ruin; defeat, (also) that which causes defeat or ruin.
   His fatal flaw was his undoing. In a sense he defeated himself.
   The extra 30 minutes could not separate the sides and led to a nerve-shredding finale that has so often been England's undoing, with a dismal record of just one win in seven shootouts at major tournaments before this. July 3, 2018, Phil McNulty, “Colombia 1 - 1 England”, in BBC Sport
3. Annulment; reversal

Etymology 2

From Middle English undoynge, undoand, from Old English undōnde (“undoing”), from Proto-Germanic *andadōndz, present participle of *andadōną (“to undo”). Cognate with Dutch ontdoend (“undoing”).

verb

1. present participle and gerund of undo