triennial sacrifice one's ancestor
祫 centers on a specific ritual: a triennial sacrifice to one's ancestors. The meaning is narrow and ceremonial, with no clear broader conceptual extension.
祫 combines 示 (altar, spirit) with 合 (join, fit), likely suggesting a ritual where ancestors are joined or brought together in sacrifice. The exact historical development is uncertain.
The left side 示 suggests a ritual altar, and the right side 合 means to join or fit together. Picture a ceremony where the family joins together at the altar to offer a triennial sacrifice to the ancestors.
For コウ, imagine a solemn ceremony where everyone bows their head low in a collective 合 (ごう) gesture of respect: the コウ reading echoes the idea of joining together in ritual.