Don't try this at home!

  Un- \Un-\ [OE. un-, on-, the unaccented form of the accented
     prefix and- (cf. {Answer}); akin to D. ont-, G. ent-, OHG.
     int-, Goth. and-. See {Anti-}.]
     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 unbend, 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.
         [1913 Webster]

  foo

     <jargon> /foo/ A sample name for absolutely anything,
     especially programs and files (especially {scratch files}).
     First on the standard list of {metasyntactic variables} used
     in {syntax} examples.  See also {bar}, {baz}, {qux}, {quux},
     {corge}, {grault}, {garply}, {waldo}, {fred}, {plugh},
     {xyzzy}, {thud}.