Coign and Headstone

Coign noun - The keystone of an arch.

Headstone and coign are semantically related. In some cases you can use "Headstone" instead a noun "Coign".

Headstone noun - A shaped stone laid over or erected near a grave and usually bearing an inscription to identify and preserve the memory of the deceased.

Coign and headstone are semantically related. Sometimes you can replace term "Coign" with "Headstone", this nouns are similar.