I mentioned earlier in a comment that Finnish words for relatives are much more complicated than the corresponding English ones. Let me expand that a bit.
I already wrote that we have a different word for uncle, depending on whether he's your mother's brother ("eno") or your father's brother ("setä"). The word for aunt is the same ("täti"), independent of whether she's your mother's or father's sister. You also need to specify whether nieces and nephews are your brother's or sister's kids (they're just called "sister's daughter", "sister's son" etc.) This caused great difficulties when Donald Duck was published in Finnish. Initially, Donald was translated as "setä" (uncle from father's side) of Huey, Dewey and Louie, and they were Donald's "veljenpojat" (nephews from brother's side). But then Don Rosa started publishing the comics expanding the history of the duck family. It turned out that Donald is actually "eno" of Huey, Dewey and Louie, and the translators were in trouble. They decided to keep using "setä" nevertheless. and only use "eno" in the historical comics, where it really matters.
In Swedish, it's important to specify whether your grandfather or grandmother is from the father's side ("farfar" / "farmor") or from your mother's side ("morfar" / "mormor"). English and German don't distinguish between them, and in Finnish we have a set of side-neutral words (which literally mean grandfather / grandmother): "isoisä" and "isoäiti", but we can also specify it if we want to ("isänisä", "isänäiti", "äidinisä", "äidinäiti").
There's an additional Finnish word which is closely associated to the words for relatives, namely "kaima" - somebody who has the same name as you. It's almost like namesake, but namesake - according to Wikipedia - means especially somebody / something that has been named after somebody. "Kaima" doesn't share this meaning - it means especially somebody who has the same name by coincidence.
Instead of godfather and godmother we have god-aunt, "kummitäti", and god-uncle-from-the-father's-side, "kummisetä".
The expression "serkun kummin kaima" (cousin's godparent's namesake) means a distant relative who you feel like you should include in your Christmas card sending list but you don't want to, or a relative who you're not sure how exactly you're related to.
Like in English, we call siblings who only share one parent with you half brothers ("velipuoli") and half sisters ("siskopuoli"). That's logical, since they share half of your blood, in a way. But we also call step parents "half parents": "äitipuoli" (lit. mother half) and "isäpuoli" (lit. father half). That makes no sense.
And to keep up with the "words and expressions they don't teach you in school" undercurrent of this blog, there is a cute almost-relative name in Finnish, which is very hard to translate: napalanko, literally "bellybutton (napa) brother-in-law (lanko)" (or maybe "brother in bellybutton"). It means a person who is two steps away from you in the sexual relation network, and as the name suggests, your "napalanko"s are men who have had sex with the same person as you (before, after or at the same time, doesn't matter). Theoretically, the same term for women would be "napakäly" (bellybutton sister in law) but it's not widely used.
The corresponding German term is much more obscene: der Lochbekannte, literally meaning "hole acquaintance". I don't even dare to think what the female term would be. With the Finnish term, it's obvious that the gender of the person you're talking about matters, that is, you need to refer to him or her as sister in law or brother in law, but in the German world view, it seems that the gender of the pivot person is more important.
I am not aware of the corresponding terms in any other language and googling failed me. Maybe it's better this way. But if this term exists in your mother tongue, or in a language you know, feel free to comment.