Dic: mainstay

• 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. 
• Cocoa is the country’s economic mainstay. 
• She is the spiritual mainstay of his life.

1. N-COUNT : usu the N of n | If you describe something as the mainstay of a particular thing, you mean that it is the most basic part of it.

2. ~ of sth | a person or thing that is the most important part of sth and enables it to exist or be successful.

... Cobuild, OALD, etc.