A mainstay is something that acts as a source of support for a community. If your hometown’s economy depends on tourists visiting every summer, you could say that tourism is the mainstay of your town.
A mainstay holds everything together, whether it’s your grandmother who acts as the anchor of your whole crazy family, a pillar that physically keeps a building from falling down, or the job that enables you to pay your rent every month. The noun mainstay is originally a nautical term meaning the rope that stabilizes two masts on a sailboat, and since the 1780s it’s been used to mean “chief support.”
a prominent supporter
a central cohesive source of support and stability
the forestay that braces the mainmast