The plural of foremast; the forward masts on ships (the front masts that hold sails).
From 'fore-' (front) + 'mast' (vertical pole). This is straightforward nautical vocabulary that evolved from Middle English and has been used since medieval times.
On large ships, the foremast was actually second in importance only to the mainmast—it's what sailors first caught sight of when spotting another ship on the horizon.
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