- Nautical. the stay that secures the mainmast forward.
- a person or thing that acts as a chief support or part: Coffee is the mainstay of the country’s economy.
- nautical the forestay that braces the mainmast
- a chief support
n.“chief support,” 1787, figurative use of a nautical noun meaning “stay which extends from the main-top to the foot of the foremast” (late 15c.), from main (adj.) + stay (n.).