Noun
main-mast (plural main-masts)
Alternative spelling of mainmast
main mast
Commissioned ships and submarines wear the White Ensign at the stern whilst alongside during daylight hours and at the main-mast whilst under way. Source: Internet
On a modern fore-and-aft rigged boat the largest sail set on the main-mast is known as the mainsail, rather than main course. Source: Internet