Your stepson is a boy or man who is the son of your husband or wife, born before you married them. He is not your own child by birth, and you may or may not have adopted him — the word says nothing about the paperwork, only about how he arrived in your family. Notice the direction this word points: you look down at him. He calls you his stepfather or stepmother; you call him your stepson. Many people avoid the word in front of the child, because it can sound like you are holding him at arm's length — they just say 'my son'. Where you do hear it is when someone needs to be exact: filling in a form, explaining a family to a stranger, or in the news ('the victim's stepson'). It is a plain, neutral word in itself, neither warm nor cold; the warmth comes from the person saying it. Written as one word, and the female match is stepdaughter.