mainstay
//ˈmeɪnˌsteɪ//
Noun
mainstaySingular
mainstaysPlural
1
A person or thing that is relied upon as a chief support or essential element.
Rice has been a mainstay of the Japanese diet for centuries.
2
(Nautical) A strong rope or cable that supports the mainmast of a sailing ship.
The sailors inspected the mainstay to ensure the mainmast was secure.