Definition from Wiktionary, the free dictionary
stepgrandson (plural stepgrandsons)
- The son of one's stepchild, or the stepson of one's child.
2009, January 23, “Susan Dominus”, in Coming Up Short as a Role Model for the Mommy Track:
- The son of an out-of-work contractor can hope for a crack someday at a Senate seat, knowing that the stepgrandson of a woman who lives in a metal-roofed shack is moving into the White House.