Oxford Advanced American Dictionary

Definition of undo verb from the Oxford Advanced Learner's Dictionary

 Oxford3000

undo

verb
undo pronunciation English ʌnˈduː undo pronunciation American ʌnˈduː
undoes
undoes pronunciation English ʌnˈdʌz undoes pronunciation American ʌnˈdʌz
undid
undid pronunciation English ʌnˈdɪd undid pronunciation American ʌnˈdɪd
undone
undone pronunciation English ʌnˈdʌn undone pronunciation American ʌnˈdʌn
 
1 undo something to open something that is fastened, tied or wrappedto undo a button/knot/zip, etc.to undo a jacket/shirt, etc.I undid the package and took out the books.
Opposite
do up2 undo something to cancel the effect of somethingHe undid most of the good work of the previous manager.It's not too late to try and undo some of the damage.UNDO (= a command on a computer that cancels the previous action)3 [usually passive] undo somebody/something (formal) to make somebody/something failThe team was undone by the speed and strength of their opponents.