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)

• fatback
• fatbacks
• fat bodies
• fat body
• fatbrained
• fat camp
• fat camps
• fat cat
• fat-cat
• fat cats
• fat chance
• fat cities
• fat city
• fat client
• fate
• fated
• fateful
• fatefully
• fatefulness
• fatefulnesses
• fates
• fat-face
• fat-faced
• fat-finger
• fat-free