I need a word to express someone that has a unhealthy obssession for one's own sister. Someone suggested me to use the word "adelphiliac", but I am pretty sure it is not a real world. There is a song by that name, and the greek roots (adelphi + philia) are in there but no dictionary or thesaurus list it.

What idiom could I use? Expressions or single-words are fine.

EDIT: in a non-sexual context.

  • Does a common (not technical) word exist in your language. Have you consulted a bilingual dictionary?
    – James K
    May 7, 2019 at 18:00
  • Mindwin, it's still not right. You need to write 'his own', 'her own', or 'their own' sister. May 7, 2019 at 19:51

3 Answers 3


"Incest" is the fairly common word for sexual relations with a close family member. There is no common word specifically referring to sisters.

Adelphiliac seems to be a nonce used in the lyrics of one song. It may have some use in psychotherapy, but it is not a word that you would expect a general speaker to understand. It would explictly refer to an incestual sexual obsession or relationship.

So you could express this exactly as you have done in your question "He is a person with an unhealthy obsession with his sister". This euphemistically implies a sexual obsession.

A non-sexual obsession would probably need to be explict:

He is obsessed with his sister's school grades.

He is obsessed with how his sister dresses.

He is obsessed with "protecting" his sister from other boys.


I couldn't find a technical psychological term in an admittedly brief search. There probably is one, but even if so, most readers would not be familiar with it and you'd have to define it anyway.

Why not just say, "he's obsessed with his sister"?

BTW I'm not clear if you mean a sexual obsession, or he's obsesses with the idea that he has to protect her, or what. You might want to make that clear in your story.

  • non-sexual context. I editted the question. May 7, 2019 at 18:03
  • @Mindwin Almost any use that implies obsession would also imply sexual obsession.
    – Andrew
    May 7, 2019 at 18:42

As other commentators have said, "obsession" can often have a sexual undertone, particularly when used to apply to people. Since you're looking for a non-sexual context, I'd recommend steering away from any word that has -phile or -philia as an ending, as many of those words also have a sexual context when applied to people (as opposed to things).

Depending on the particular concerns of the brother, an appropriate way to describe him might be as an "overprotective brother."

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