linchpin
US /ˈlɪntʃ.pɪn/
UK /ˈlɪntʃ.pɪn/
1.
chốt
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:
:
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Woodford is the linchpin of the British athletics team.