mainstay
noun
[ ˈmeɪnsteɪ ]
• a person or thing on which something else is based or depends.
• "farming is the mainstay of the rural economy"
Similar:
central component,
centrepiece,
prop,
linchpin,
cornerstone,
pillar,
bulwark,
buttress,
chief support,
backbone,
anchor,
foundation,
base,
bastion,
tower of strength,
key player,
sinew,
right-hand man/woman,
right arm,
Atlas,
• a stay that extends from the maintop to the foot of the foremast of a sailing ship.