mainstay:
(plural: ‘mainstays‘; pronunciation: ‘main…stay’)
Apart from several other meanings/definitions…
a chief supporter of something, such as a political party, a common cause, etc.,

the mainstays of a protest
e.g.
Our high school teacher is the mainstay of our corruption-free community!
John used to be one of the mainstays of Greenpeace organisation, organising demonstrations and protests until he was hit by a car lost both his legs.
When policies of a political party are changed, the mainstays try to stop those changes, and when they can’t stop the changes, they stray away.
The team lost its confidence as three mainstays got injured in the field and are sent away.
For a news article in which shows us how we come across this word in our daily browsing, please click here, for a sports article in which we see this word being used to refer to a player, please click here & for another sports article in which we find this word being used for a player as well as his performance, please click here and for an Islamic religious article in which a brave lady is referred to as a mainstay of Hijrah, please click here.

(wheat is the mainstay)
Note: ‘Mainstay’ is more commonly used of things that are very important and that give strong support, e.g. “Sugar cane is the mainstay of our country’s economy.” and “Rice and potato are the mainstays of our diet.”, and ‘mainstay’ is also used to refer to a strong rope that supports the main sail of a sailing ship. For a news article that shows us how this word is used to refer to an important building, please click here.
