/ ʌnˈduː; NAmE / verb ( un·does / ʌnˈdʌz; NAmE / un·did / ʌnˈdɪd; NAmE / un·done / ʌnˈdʌn; NAmE /) [ vn ]
1.
to open sth that is fastened, tied or wrapped :
to undo a button / knot / zip, etc.
to undo a jacket / shirt, etc.
I undid the package and took out the books.
OPP do up
2.
to cancel the effect of sth :
He 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 ] ( formal ) to make sb/sth fail :
The team was undone by the speed and strength of their opponents.
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WORD ORIGIN
Old English undōn (see un- , do (I)).