main-topgallant
/ˌmeɪntɒpˈɡalnt/ /ˌmeɪntəˈɡalnt/Nautical
noun
A topgallant situated just above the head of the maintopmast. Chiefly in compounds: main-topgallant-crosstree, main-topgallant-masthead, main-topgallant-sail, main-topgallant-yard, etc. main-topgallant-mast noun the mast above the maintopmast.
Origin
Late 16th century. From main + topgallant.