Words for family members and other relatives in Finnish.
Singular form vanhempi means "older" and "the elder"
boy / son
Finnish boy (poika) is the same as son (poika) and that someone is someone's son has to be red from the context
Genderless way to say to have brother(s) and/or sister(s)
Sisar less used as it can be confused with genderless sisarus
Cousin from your mother's side, rarely used
Cousin from your father's side, rarely used
What cousins' childs are to each others.
Literally "sugar cousin" and "quarter cousin". This is what cousins' grandchildren are to others
Literally "fragment cousin". This is what cousin's great grandchildren are to each others
Literally means "family's family" or even "extended family's family" and is used of those who are distantly relative
Literally "brother's son"
Literally "sister's son". Siskonpoika is also possible variation as sisaren- can be mixed to the next...
Can be used if you have more siblings and you are pointing like in a family party, that "that is one of my siblings' son" and not really knowing is it your brother's or sister's son, or just when you don't want to say if he is your brother's or sister's son, or even when you have only one sibling so the fact who's son he is can't be missed.
Literally "sister's daughter". Siskontyttö is also used which means literally "sister's girl" also siskontytär "sister's daughter" as this too can be confused with previous.
Literally means "brother's daughter"
Again can be used as genderless way to say "one of my siblings' daughter" just like in sibling's son above.
Singular is not really used
Some families make a difference of father's and mother's parents by using synonymes like mummu, mummo, mummi, mamma etc. that all mean "grandmother". They can say that their mother's mother is mummi and father's mother mummo. Same applies to grandfather, only then is used words like vaari, ukki, ukko, äijjä, äijji, pappa etc. which all mean "grandfather" respectively.1
Basicly just add iso- (big) in front of the word and you get one generation backwards every time.
Usually we don't separate genders beyond two generations so this literally means "child's child's child".
Relatives from marriage
Spouse's sister, brother's wife or spouse's brother's wife
Spouse's brother, sister's husband or spouse's sister's husband. Older name suoveri "swampblood" isn't really used nowadays
Daughter's husband. Naming kotivävy "home son-in-law" is used for a son-in-law that lives in his wife's home.
Used when speaking of your spouse's parents.
Note, mies means "man" so if it is not known that we are talking about someone's husband, it is correct to use avio- in front of it.
Names used in folk-poetry
Husband's brother (only!)
Husband's siter (only!)
Spouse's brother, sister's husband or spouse's sister's husband
These notes are written by Karri Anttila from his perspective, so "I" and "my" refer to Karri.
These notes are mainly my thoughts and most likely have a strong influence from the Häme dialect, and therefore cannot be read as a grammar/facts. A speaker from the Savo dialect area would say many things differently.
1. I have a friend who calls his grandfather ukki and his grandmother's (still-living!) father vaari making a difference between these two gentlemen. My father's mother is mummu (to me) and my mother's mother was mummo, though my parents were originally from different dialect areas so the difference is understandable.
This is mostly family habit or way of speaking and also a wish from grandparents, my grandmother couldn't stand mamma as she used to call her mother that way, which is why I call my grandmother mummo and then again her mother to me is [her first name + mummu]. So my grandmother's mother (from father's side) to me is Silja-mummu and my mother's grandmother is Claudia-mummo (again, she is from a different dialect area so we have mumm- body with -o and not -u).
Very few people actually use isoäiti/isoisä when speaking of their grandparents but use other words that are considered as synonyms. De jure there is no difference between mother's mother and father's mother as a word but it seems that usually the difference appears at last when the grandchild learns to speak.
2. In my experience the word tytär (daughter) is usually turned into tyttö (girl) when combined with other words, especially when in the genetive form. For example:
tyttärentytär "daughter's daughter" can be turned into tytöntyttö which basically means "girl's girl"
This happens to happen with "sister" sisko/sisar too. For example:
sisarentytär "sister's daughter" (or possibly "sibling's daughter" as the difference has to be read from the context) can be turned into siskontytär (which makes it recognizable from "sibling's daughter") or into sisarentyttö meaning "sister's(/or sibling's, again) girl" and ultimately siskontyttö
I think all of these versions can be genuinely used in formal or in common speech/text.
There are also tons of different dialect and loan words for sister/girl in Finnish that can't be used in formal text but can be used in speech. In my family we usually call sisters (anyone who has a sister) as likka which is a loan word from Swedish flicka and means, again, "girl". Therefore if my sister would have a son, for example, I would call him likanpoika which would basically be "girl's son".