balustrade vs barbican

balustrade

noun
  • A row of balusters topped by a rail, serving as an open parapet, as along the edge of a balcony, terrace, bridge, staircase, or the eaves of a building. 

barbican

noun
  • A fortress at the end of a bridge. 

  • An opening in the wall of a fortress through which the guns are levelled; a narrow loophole through which arrows and other missiles may be shot. 

  • A tower at the entrance to a castle or fortified town 

  • A temporary wooden tower built for defensive purposes. 

How often have the words balustrade and barbican occurred in a corpus of books? (source: Google Ngram Viewer )