un ‧ do /ʌnˈduː/ BrE AmE verb ( past tense undid /-ˈdɪd/, past participle undone /-ˈdʌn/, third person singular undoes /-ˈdʌz/) [transitive]
[ Word Family: verb : ↑ do , ↑ outdo , ↑ overdo , ↑ redo , ↑ undo ; noun : ↑ deed ≠ ↑ misdeed , ↑ do , ↑ doing ; adjective : ↑ done , ↑ overdone , ↑ undone ]
1 . to open something that is tied, fastened, or wrapped:
The screws can be undone by hand.
I undid the package carefully.
undo your jacket/shirt/bra etc
He undid his coat.
2 . to try to remove the bad effects of something you have done:
We cannot undo the damage of a lifetime in only 30 days.
If a medicine is taken again too soon, it may undo all the good that has been done.
3 . technical to remove the effect of your previous action on a computer