An inseparable verbal prefix or particle. It is prefixed: (a) To
   verbs to express the contrary, and not the simple negative, of the
   action of the verb to which it is prefixed; as in uncoil, undo, unfold.
   (b) To nouns to form verbs expressing privation of the thing, quality,
   or state expressed by the noun, or separation from it; as in unchild,
   unsex. Sometimes particles and participial adjectives formed with this
   prefix coincide in form with compounds of the negative prefix un- (see
   2d Un-); as in undone (from undo), meaning unfastened, ruined; and
   undone (from 2d un- and done) meaning not done, not finished. Un- is
   sometimes used with an intensive force merely; as in unloose.