Stepparent

Within a family, a stepparent was the spouse of a parent, but not the biological parent of the children. They might also be termed a stepmother or stepfather.

Doris Lethbridge-Stewart was Kate Stewart's stepmother. (PROSE: Lucy Wilson and the Bledoe Cadets, Acceptance, and then Understanding)

Professor Howard Foster was an archaeologist and Peri Brown's stepfather. (TV: Planet of Fire)