{i} strong rope supporting the mainmast of a sailing vessel (Nautical); chief support, something which is greatly relied upon
If you describe something as the mainstay of a particular thing, you mean that it is the most basic part of it. Fish and rice were the mainstays of the country's diet This principle of collective bargaining has been a mainstay in labor relations in this country. a an important part of something that makes it possible for it to work properly or continue to exist
a central cohesive source of support and stability; "faith is his anchor"; "the keystone of campaign reform was the ban on soft money"; "he is the linchpin of this firm"