noun
Etymology: Middle English, from gerund of undon to undo — more at undo
1. : loosing , unfastening
2.
a. : a bringing to naught : destruction , ruin
cocaine … leads to his complete undoing by destroying his mental equipment — A.C.Morrison
b. : a cause of ruin
a redhead who was to prove my undoing — C.C.Wertenbaker
3. : the reversal, cancellation, or annulment of something done : reinstatement of a condition existing previous to some act or accomplishment
would settle for nothing less than the complete undoing of his country's calamitous defeat and humiliation