lynchpin• You blag a meeting with the band's lynchpin, organist Clint Boon.• James in particular, the man earmarked as the lynchpin in the tactical plan, was not living up to expectations.• Regular brushing is the lynchpin of all good dental hygiene.• The first of these is the lynchpin of the argument.• The dollar was the lynchpin of the Bretton Woods system.