linchpin /linchˈ or linshˈpin/

1. A pin used to keep a wheel on its axle
2. A person or thing essential to a plan, organization, etc (figurative)

• crank
• crankcase
• crankcases
• cranked
• crankhandle
• crankier
• crankiest
• crankily
• crankiness
• crankinesses
• cranking
• crankle
• crankled
• crankles
• crankling
• crankness
• cranknesses
• crank pin
• crank pins
• cranks
• crankshaft
• crankshafts
• crank-sided
• crank up
• cranky