I did look up the definition in the Hebrew dictionary. (Not the English dictionary of course, because the man wrote it in Hebrew, so before I can try to translate his thought into the different language of English, I must look in the dictionary of his own language first for the word he used and then I can try to translate it equivalently to my own language.) So to look up the word he originally used, since I don't speak or understand Hebrew, I have to have someone to translate. And that is where the concordance comes in. It is a translator so I can look up the original word he used and see what it meant in his own language to then determine if perhaps the man who translated to English may not have used the best definition to convey the authors original intent.
By the way, even in English, a cap or top stone does not always mean a grave marker. It can mean in most English speaking persons minds a stone that completes a thing being constructed, which could be a stone fence or some stone construction other than a stone to write an epitaph on. And I say this having not even looked up these words in English, because English didn't even exist at the time the man wrote the verse, so English was in no way foundational to his writing. It is only foundational to my own understanding OF his writing.
What does the Hebrew dictionary say it means? Here's the English definition that I'm going by to understand that verse.
head·stone
ˈhedˌstōn/
noun
- a slab of stone set up at the head of a grave, typically inscribed with the name of the dead person.