Definition of mizzen topgallant in US English:

mizzen topgallant

noun

Nautical
  • A topgallant situated just above the head of the mizzen-topmast. Chiefly attributive, especially in "mizzen topgallant mast"noun the mast above the mizzen-topmast.

Origin

Late 17th century; earliest use found in MSS House of Lords. From mizzen + topgallant.