n. 25B6; verb
he undid another button : UNFASTEN, unbutton, unhook, untie, unlace; unlock, unbolt; loosen, disentangle, extricate, release, detach, free, open; disconnect, disengage, separate.
they will undo a decision by the law lords : REVOKE, overrule, overturn, repeal, rescind, reverse, countermand, cancel, annul, nullify, invalidate, void, negate; Law vacate; formal abrogate.
she undid much of the good work done : RUIN, undermine, subvert, overturn, scotch, sabotage, spoil, impair, mar, destroy, wreck, eradicate, obliterate; cancel out, neutralize, thwart, foil, frustrate, hamper, hinder, obstruct; Brit. throw a spanner in the works of; informal blow, put the kibosh on, foul up, muck up; Brit. informal scupper; N. Amer. informal rain on someone's parade.
fasten, ratify, enhance.