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)

• porthouse
• portico
• porticoed
• porticoes
• porticos
• portier
• portiest
• portigue
• portigues
• porting
• portion
• portioned
• portioner
• portioners
• portioning
• portionist
• portionists
• portionless
• portions
• portière
• portières
• portland
• Portland
• Portland arrowroot
• Portland cement