From Longman Dictionary of Contemporary Englishstepmotherstep‧moth‧er /ˈstepmʌðə $ -ər/ ●●○ noun [countable] SSFFAMILYa woman who is married to your father but who is not your mother
Examples from the Corpus
stepmother• Jean had come to New York with his father and stepmother, but he and the stepmother had been at daggers drawn.• My future stepmother has a pair on her, no doubt about it.• One of them, Merovech, attempted to outwit his stepmother by marrying Sigibert's widow, Brunhild.• His stepmother told him to hurry up.• Even through the laughter came the whistle of my stepmother.• And that means millions of stepmothers in charge of new families.• They had to explain to their stepmother Rose what Monaghan Day was. 