The Collaborative International Dictionary of English v.0.48:

Lockup \Lock"up`\,
   1. n. A place where persons under arrest are temporarily
      locked up; a watchhouse; a jail.
      [1913 Webster]

   2. The act or state of temporary imprisonment in a lockup[1].
      [PJC]

   3. A malfunction in a machine having moving parts, such that
      the moving part cannot move; a seizure.
      [PJC]

WordNet (r) 3.0 (2006):

lockup
    n 1: jail in a local police station
    2: the act of locking something up to protect it [syn:
       locking, lockup]