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

Oxford3000

undo

verb
ʌnˈduː
 
; ʌnˈduː
 
undoes
ʌnˈdʌz
 
; ʌnˈdʌz
 
undid
ʌnˈdɪd
 
; ʌnˈdɪd
 
undone
ʌnˈdʌn
 
; 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 up
2 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.