capstone of a cist; dolmen burial chamber
Archaeological term referring to the stone lid of a cist (stone coffin) or the chamber of a dolmen. Rare in everyday conversation.
During the excavation, a capstone was found in perfect condition.
The capstone of this site is engraved with line drawings.
Compound of 石 (いし, 'stone') and 蓋 (ふた, 'lid'), literally 'stone lid'. The reading いしぶた is a straightforward combination.