Noun
The principal mast in a ship or other vessel.
Source: Webster's dictionaryThe ship had a smaller topsail on the mainmast above the mainsail and on the foremast above the foresail. Source: Internet
The vessel had three masts: a mainmast, a foremast, and a mizzenmast. Source: Internet
This included removing the Exocet missile system and EW equipment, and fitting a funnel aft of the mainmast to replace the waterline exhausts. Source: Internet