Is my mother's step-father, my step-grandfather? To what extent is it usual to extend the prefix 'step'? Can we speak of 'step-cousins', step-aunts and step-uncles etc? If we can it must make for considerable complication in how such relationships are defined. Answer Of the combining form step- , Oxford Dictionaries only says: denoting a relationship resulting from a remarriage Past immediate step-parents or step-siblings, I no longer find the distinction useful. Introduce your mom's stepfather as "My mom's stepfather." Likewise with your stepmom's sister, your aunt's stepdaughter, and so forth.