capstone vs coping stone

capstone and coping stone both are nouns.

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

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

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

Other synonyms of capstone include copestone, stretcher.

capstone (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