Definition from Wiktionary, the free dictionary
stepgrandchild (plural stepgrandchildren)
- The stepchild of one's own child.
2007 February 7, Matthew L. Wald, “M. Lamar Muse, 86, Dies; Led Southwest Airlines”, in New York Times:
- Other survivors are […] three grandchildren; one great-grandchild; two stepdaughters; and two stepgrandchildren.
- The child of one's stepchild.