copestone vs coping stone

copestone and coping stone both are nouns.

Word	Noun	Adjective	Verb	Adverb
copestone	Yes	No	No	No
coping stone	Yes	No	No	No

As nouns, copestone and coping stone are synonyms defined as:

copestone and coping stone: a stone that forms the top of wall or building

Other synonyms of copestone include capstone, stretcher.

copestone (noun)	coping stone (noun)
a stone that forms the top of wall or building	a stone that forms the top of wall or building
a final touch; a crowning achievement; a culmination