un- 2
pref.1. To reverse or undo the result of a specified action: unbind.
2. a. To deprive of or remove a specified thing: unfrock.
b. To release, free, or remove from: unyoke.
3. Used as an intensive: unloose.
[Middle English, from Old English on-, alteration (influenced by un-, not) of ond-, and-, an-, against, opposing; see ant- in the Appendix of Indo-European roots.]