grandcousin means the grandchild of a first cousin, or the first cousin of a grandparent; first cousin twice removed. Lexicurio rates it Sui generis — a strength score of 90 out of 100.
Etymology
From grand- + cousin.
noun
- The grandchild of a first cousin, or the first cousin of a grandparent; first cousin twice removed.“Just recently I learned that the star of the Johns Hopkins lacrosse team is the great-grandson of my first cousin Myrtle, which I suppose makes him my great-grandcousin.”