1. (noun) the central building block at the top of an arch or vault

• key
• keystone

2. (noun) a stone that is used to mark a grave

• gravestone
• tombstone

1. (noun) the central building block at the top of an arch or vault

• building block

2. (noun) a stone that is used to mark a grave

• memorial
• monument
• stone

1. (noun) the central building block at the top of an arch or vault

• coign
• coigne
• quoin