mainstay
noun uk/ˈmeɪn.steɪ/ us/ˈmeɪn.steɪ/
the mainstay of something …的支柱；…的主要依靠
the most important part of something, providing support for everything else
Cattle farming is the mainstay of the country's economy. 养牛业是这个国家的经济支柱。
The white blouse will be the mainstay of your wardrobe this summer. 白色衬衫将是今年夏天你衣橱里的主要服装。