To reverse, as what has been done; to annul; to bring to naught.
- To reverse or erase; annul: impossible to undo the suffering caused by the war.
- To untie, disassemble, or loosen: undo a shoelace.
- To open (a parcel, for example); unwrap.
- To cause the ruin or downfall of; destroy.
- To throw into confusion; unsettle.
- Obsolete To solve or interpret; unravel.
- To come open or unfastened.