say it: uhn-DOO-ing
undoing is a noun meaning "an act that makes a previous act of no effect (as if not done)". It carries 2 recorded senses.
an act that makes a previous act of no effect (as if not done)
loosening the ties that fasten something
“the tying of bow ties is an art; the untying is easy”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for undoing come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.