The Collaborative International Dictionary of English v.0.48:

Customhouse \Cus"tom*house"\ (-hous`), n.
   The building where customs and duties are paid, and where
   vessels are entered or cleared.
   [1913 Webster]

   Customhouse broker, an agent who acts for merchants in the
      business of entering and clearing goods and vessels.
      [1913 Webster]

WordNet (r) 3.0 (2006):

customhouse
    n 1: a government building where customs are collected and where
         ships are cleared to enter or leave the country [syn:
         customhouse, customshouse]