v.tr. (3rd sing. present -does; past -did; past part. -done)
1. a unfasten or untie (a coat, button, parcel, etc.). b unfasten the clothing of (a person).
2 annul, cancel (cannot undo the past).
3 ruin the prospects, reputation, or morals of.
Etymology: OE undon (as UN-(2), DO(1))