the most important thing or person in a system, plan etc, which everything else depends on:
• The consumer is the linchpin of the economy.
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linchpin UK US (also lynchpin) /ˈlɪntʃpɪn/ noun [C]
► the most important member of a group or part of a system, that holds together the other members or parts or makes it possible for them to operate as intended: linchpin of sth »
Consumer spending is the linchpin of the economy.
Financial and business terms. 2012.