noun
stepson
Refers to a son from a spouse's previous relationship. The term is neutral and factual.
彼の継息子は来年高校を卒業する。
His stepson will graduate from high school next year.
Compound of 継 (まま, 'step-', as in step-relationship) and 息子 (むすこ, 'son'). The prefix 継 is used in several kinship terms for step-relations.