It seems a pity to let perfectly usable words become obsolete or thought to be too old when they fill a need to not be so specific and ease the lack of knowledge of the family relationship. Of course, I am ancient, and do not always appreciate the need to change to modern, especially when nothing fills in the hole left.
A word like onkel wasn't used when I grew up, and I've never even heard very old people use it (except jokingly or in special cases, like Onkel Toms stuga 'Uncle Tom's cabin'), so I don't really feel the loss. In fact, to me, keeping the traditional way of naming uncles as either morbror or farbror feels more valuable – rather than following the same pattern that exists in English or French. What I mean is that if we did use words like onkel (a loan word to begin with), we'd be at risk of losing our own words, which feel much more valuable to me. And when you grow up like I did within a system where you have to choose between farbror and morbror, I think you tend to get very used to that and not miss a neutral word. Like it seems that most native speakers of English don't miss a neutral verb form which would cover both present and present continuous.
Yeah, I had a pretty similar discussion with Zmrzlina here: https://www.duolingo.com/comment/5709711$comment_id=7691485
The dictionary unfortunately does not show if words are in use anymore :D
Sorry if it was already mentioned and i missed it, but what do you use when the "grandma" or "aunt" or whatever is more of a honorary title and they are actually not really your family?
I'm not entirely sure what context you're talking about, but if you mean for example a mother referring to her friend Alice as "auntie Alice" while talking to her child, the word you would use is "tant". As for "grandma", if someone were to refer to themselves as "grandma/grandpa" to sound more approachable or something, you would probably use "mormor" and "farfar", I'd guess it's something psychological because of the repeated sounds.
You don't really use family words as honorary titles that often in Sweden, so it's hard for me to say for certain because I'm not sure what situation it would show up in.
Oh, sadness! We have two family friends whom we referred to always as Aunt and Uncle. Except they weren't. But they were at every family event, every holiday dinner, just no blood relation. It's as though they were informally adopted by our family.
Except, turns out they both had their own families too!
Chiming several years later, but sometimes, if needed be, I denote such a person as "ingift" (literal: in-married). So I'd say "min ingifte morbror" to denote my mother's sister's husband. Most often it's not necessary to do so, but it has been been needed from time to time and "ingift" is an acceptable way to define an aunt/uncle which isn't so by blood, only due to marriage.