top·mast /ˈtɑpˌmæst, məst/
  中桅
  Top·mast n. Naut. The second mast, or that which is next above the lower mast, and below the topgallant mast.
  ◄ ►
  topmast
       n : the mast next above a lower mast and topmost in a
           fore-and-aft rig