A son of a grandchild.

Synonym of great-uncle

The father of someone's great-grandparent.

The mother of someone’s great-grandparent.

A longcase clock.

Synonym of great-aunt / A sister of grandparent

A grandson of one's sibling; a son of one's nephew or niece. (Brother's grandson: fraternal grandnephew. Sister's grandson: sororal grandnephew.)

A parent of a grandparent; a grandparent of a parent.

A clause or section, especially in a law, granting exceptions for people or organisations who were affected by previous conditions.

(informal, Scotland, Northern England) grandfather