1. (initialism) .  '''A'''ir '''P'''ost '''O'''ffice (both Army and Air Force).
  2. (initialism) .  '''A'''rmy '''P'''ost '''O'''ffice.
  3. (initialism) .  '''A'''ir Force '''P'''ost '''O'''ffice.
  4. Adjective.  (biochemistry, of a protein) In an inactive, unbound state.

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This entry was last updated on RefTopia from its source on 3/20/2012.