coping stone vs capstone

coping stone and capstone both are nouns.

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

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

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

Other synonyms of coping stone include copestone, stretcher.

coping stone (noun)	capstone (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