the.com/headstone

means The engraved marker set at the head of a grave to identify who's buried there and keep their name in use a little longer.

from Straightforward compound of 'head' (the top or main end) and 'stone' — it literally marks the head end of the grave, the spot above where the deceased's head lies. The word shows up in English going back several centuries, originally covering any stone set upright at the head of a grave; the structural sense of 'stone that caps or anchors a building' (a 'headstone' of a wall or arch) is a related, older architectural use, which is likely why the burial sense borrowed such solid, foundational language for something meant to outlast everyone who reads it.