Pretty much in the title but to make it more explicit:

  • You have a child X
  • X has a half-sibling Y
  • You are not in a relationship with either of Y's parents (formerly you were with one of them to produce X)

What do you call Y with respect to yourself?

  • 1
    Why would there be a word for someone who isn't related to you?
    – tchrist
    Commented Feb 13, 2020 at 3:20
  • 1
    @tchrist - Because they are indirectly related in a pretty straightforward manner? Half siblings are common enough that it could be useful to have such a word.
    – nnnnnn
    Commented Feb 13, 2020 at 3:47
  • 2
    @tchrist Why would there be a word for throwing someone out a window? Yet, there is one. There are hundreds of thousands of words, so it does not seem strange to me to wonder if there is one that applies here. Commented Feb 13, 2020 at 5:21
  • 1
    @nnnnnn There are many close non-blood relationships which perhaps should have names but don't. For instance what do you call your children's in-laws? That can be a really close relationship, particularly as you can share grandchildren with their parents-in-law. I'm really surprised that there isn't one for that relationship given the political importance of arranged royal marriages in the past.
    – BoldBen
    Commented Feb 13, 2020 at 5:43
  • 1
    @tchrist - My child's (hypothetical) half-sibling isn't related to me by blood, but it is still a relationship in the "connection" sense, and it's a fairly close connection given my child is extremely closely related to both of us. Cousins' cousins are much more distant and irrelevant connections, but it's fairly common for half-siblings to live in the same house, so there are reasonably common, practical applications for this my-child's-sibling word, if it existed. Obviously we can all get by without it, but that's true of lots of real words.
    – nnnnnn
    Commented Feb 13, 2020 at 6:51

2 Answers 2


There is no standard word for this relationship. Kinship is not usually treated as transitive -- your cousins may have cousins with whom you share no ancestor, and thus you are not usually considered related to such cousins' cousins.

"My ex's kid" is probably an easily-understood shorthand. It does not sound as warm as might be ideal, but I suspect "my daughter's (half-)sister" would prove more distracting than helpful.

If you are bound to this child by care or affection, a word like "niece" or "step-daughter" might be employed, though such terms might be misunderstood as presumptuous as well. The idea of a niece/aunt relations is quite traditionally very flexible, and used outside of its literal meaning.

  • Thanks Mike. You and I are of the same mind. I posted this question hoping someone knew something I did not know.The situation in particular is that I spend 'a lot of time' with my ex's kid in a mentorship role (the kid also being my own child's half sibling). Both "my ex's kid" or "my daughter's (half-)brother" come off sounding rude or harsh no matter what tone I put it in. (I'll click the 'accept answer' in a day if some savant doesn't come out of the wood works with some obscure 18th century term.)
    – Lan
    Commented Feb 13, 2020 at 13:02
  • @Lan I think the savant is stuck in the wood works.
    – Conrado
    Commented Jul 8, 2023 at 2:48
  • This is a good answer. Although in practice if your ex is called e.g. Michelle, it's more polite to say "Michelle's child" than "my ex's child", at least to people who know Michelle. But the OP doesn't give a context.
    – Stuart F
    Commented Jul 8, 2023 at 10:57

There is no term for such a relationship. For all intents and purposes, you and Y are not related at all. For below, Foo is you, Bar is the other parent of X, and Qwerty is the remaining parent of Y.

  • X is Foo's child.

  • Y and Foo have no relation.

  • X and Y are both children to Bar.

  • X is a stepchild to Qwerty (only if Bar and Qwerty are married).

  • Y is X's half brother or half sister.

Hope this helps.

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