Other forms: undone, undoing, undid, undoes
To undo is to cancel the last thing you did. Press undo, undo it, the undo button.
In software, undo is one of the most valuable commands ever invented, and the keyboard shortcut is among the few most people know. The general sense is to reverse or unfasten: undo a button, undo the damage, undo the good work of a decade. Note undone, which means both unfastened and ruined — I am undone is old-fashioned for I am destroyed; and that redo is undo's counterpart.
1verbundoTo cancel the last thing you did.
“If you delete a paragraph by mistake, just click undo to get it back.”
2verbunfastenTo unfasten or reverse something.
“It took about a decade to undo the damage of one policy.”
undo is a reversing.
Old English ondon is the reversing un- plus do, and it is as old as the language. The computing sense arrived in the 1970s and is one of the plainest English words in the whole vocabulary of software.
Middle English
undōn
English, today
undo
From Middle English undōn. From Middle English undōn, from Old English ondōn, from Proto-West Germanic andadōn (“to undo”), equivalent to un + do. Cognate with West Frisian ûndwaan, ûntdwaan (“to undo; rid”), Dutch ontdoen (“to undo”).
Etymology from Wiktionary, CC BY-SA