Stepchild

1. (n.) A bereaved child; one who has lost father or mother.

2. (n.) A son or daughter of one's wife or husband by a former marriage.

Thesaurus Entries

child, daughter, descendant, foster child, grandchild, granddaughter, grandson, heiress, offspring, scion, son, son and heir, sonny, stepbrother, stepdaughter, stepfather, stepmother, stepsister, stepson