Special words to describe specific relationships?

Swedish has mormor/morfar/farmor/farfar, where "mor" = mother and "far" = father. Mothermother, motherfather, fathermother, fatherfather. Now you know exactly which grandparent is being discussed.

The radio show I co-host http://www.waywordradio.org/your-childs-in-laws/ and http://www.waywordradio.org/names-for-your-childs-in-laws/.

Australian Aboriginal languages have kinship systems far more detailed than English. Random example (and there is a LOT of diversity between language groups): Here is a family tree in http://bininjgunwok.org.au/wp-content/uploads/2011/11/kin-generation-chart.jpg (the abbreviations are fairly straightforward, Z means sister). Distinctions can include not only gender (as in English), or age (as in Chinese), but also matri- vs patrilineal relationships, harmonic vs disharmonic generations (see how, in the Bininj Gunwok example, generations +2, 0 and -2 share many terms), skin, moiety, and more... Categories are conflated or differentiated in ways that they aren't in English. For example, in the bottom left of the Bininj Gunwok diagram, your son's daughter (SD) and son (SS) are both mawa, but your daughter's daughter (DD) and son (DS) are mamamah. In traditional Aboriginal society, everyone has a kinship relation to you. Kinship governs who you can speak to, who you marry, which language you speak, where your country is. Many languages even incorporate kinship into their pronouns or verbs, so that when you talk about two men doing something, you don't just say "They did x" you say "Those two male non-siblings did x". I'm not at all an expert and may have some details wrong, but basically yeah, every Aboriginal language has a lot of very specific words for very specific relationships.

My sister's sister-in-law and I call each other sisters-in-law squared.

Spanish also has concuñado/a, (literally "co-brother/sister-in-law) which is a spouse of your spouse's siblings. There's a nice symmetry to the category, because at a typical family gathering, for example, you'll often have a core group of siblings, and then all their married-in spouses who are socially all on the same slightly subordinated/peripheral level.

"Metamour" (the significant other of your significant other, who you are not romantic with as well) has come up in recent years in the polyamory community. (Along with "compersion" or "frubble" meaning the opposite of jealousy--that you're happy about their relationship even though you are not dating both of them). But beyond that, I hear ya. What do I call my relatives' relatives?

Spanish has compadre and comadre, for the relationship between people who parents and godparents of the same person. (i.e. If I were the godmother of your kid, I would be your comadre and you would be my comadre. Your baby-daddy would be my compadre, and I would still be his comadre. The godfather would be compadre to both you and your baby-daddy).

In Norwegian, there is -farfar, farmor, mormor, morfar (as Lyn Never explains above, same in Swedish) -oldefar, oldemor (great-grand-father, great-grand-mother?) -tipp-oldefar, one generation older -tipp-tipp-oldefar, another above there again -tipp-tipp-tipp... you get it. All the way back to a single celled amoeba. -"fetter" is your male cousin -"kusine" is your female cousin -"søskenbarn" is the Norwegian translation of English "cousins", literally means "sibling's kids" -I think Sweden has a bit different definitions but with same words, which is a bit confusing -grand-onkel, grand-ucle, grand-nephew, grand-whoemever, its the same in English isn't it? Your parent's uncles/aunts or similar direction. Add grand- multiple times for branching out. As in grand-grand-grand-grand-grand-aunt. Which would be quite a stranger, and probably very dead, don't talk to her and don't drink the green bubbling, smoking liquid she offers you. -"tremenning" is your cousin once removed ( three lines away) -"firmenning" is your cousin twice removed (four lines away) -"fem-menning" is your... you get it. there's a word for EVERYONE ON THE PLANET! We're all n-mennings. -"sviger" is in-law-prefix, as in sviger-mor (in-law mother) sviger-far (in-law dad), sviger-sønn (son) (etc etc) -"svoger" is a sibling of someone you're married too or the other way around -"step"-someone and "half"-someone, i suppose is in English too right? Your example above would then be you where talking to your awesome "svoger-sisters's svoger-brother". And if you said that in a social setting in Norway everyone would be very quiet and thinking really hard for two minutes. And then go "m-hmmmmm"

aburo - younger sibling egbon - older sibling (Yoruba)