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)

• overlard
• overlarded
• overlarding
• overlards
• overlaunch
• overlaunched
• overlaunches
• overlaunching
• overlay
• overlaying
• overlayings
• overlays
• overleaf
• overleap
• overleaped
• overleaping
• overleap oneself
• overleaps
• overleapt
• overleather
• overleathers
• overleaven
• overleavened
• overleavening
• overleavens