Mainstay
Mainstay is a noun that denotes a person or thing acting as a principal support or indispensable element of a system, organization, or activity. In nautical usage, the term originally referred to a strong rope or chain that secures the main mast and helps stabilize the vessel’s rigging. Because of this stabilizing function, the word later acquired a broader metaphorical sense as anything that provides essential support.
Etymology: The word comes from Middle English mainstay, from main meaning "chief" and stay meaning "rope or
Usage: Mainstay is commonly used to describe a person, organization, or thing that remains a reliable source
Notes: It is a straightforward, widely understood term that emphasizes central importance and reliability without connotations