watch·tow·er /ˈwɑʧˌtaʊr, ˈwɔʧ-/
  崗樓
  Watch·tow·er n. A tower in which a sentinel is placed to watch for enemies, the approach of danger, or the like.
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  watchtower
       n : an observation tower for a lookout to watch over prisoners
           or watch for fires or enemies