Just like language forms the basis of a relationship, a relationship - two people speaking to one another - is one of the most integral components of language. Relationships aren't just important so that language can happen - as social creatures, forming, maintaining and keeping track of relationships easily takes up most of our attention and time in our lives. In order to help us organize our complicated social networks, intricate systems for naming the people closest to us are developed over time. The system used for describing family member relationships is called a kinship system.
By analyzing the linguistic patterns in these kinship systems, we can learn a lot about how people interact with one another and which kinds of relationships hold important significance. For example, certain patterns can show us which uncle is like a second father, or which cousins are marriageable.
One of my favorite relationship terms occurs in the Russian kinship system, where there is a unique term for your wife's sister's husband (EWZH), свояк svoyak. As a sister of many sisters, it's pretty obvious to me why husbands to two sisters would have a special bond. The support group for all the men married into our family has been a long standing joke, usually brought up after one of us bursts into tears over seemingly nothing.
This past week, I've been working hard on collecting and organizing the kinship system in Chuvash. Unfortunately, it's fading out of use, and many people, even those fluent in Chuvash didn't learn or use the system growing up. According to ancient Chuvash beliefs, it was considered dangerous to call family members by name. To protect them from evil spirits, you called your sister 'sister', your niece 'niece', and so on, not only when talking to them, but when talking about them as well. Husband and wife called each other by their first-born child's name "Sasha's mother" or "Sasha's father," and there are stories of husband's and wives after thirty years of marriage not being able to recollect the other's real name!
Chuvash is interesting in that it differentiates gender (parent's have unique names, mother and father); it differentiates maternal and paternal lines (your mother's mother and your father's mother have unique names) and it differentiates birth order (your older brother and your younger brother have unique names). To make it even more complicated, the system changes between three perspectives, so that the word I use to talk about my mother (анне, annye) is different from the word I use when talking about your mother (аннӳ) or about his mother (амăшĕ, amuhzheh).
It's not impossible to keep track of though, the Chuvash system is filled with patterns which illuminate special relationships. One of my favorite's, I've drawn using KinOath below:

In this diagram, circles represent females, triangles represent males, and the black square in the center represents Ego or self. Connecting lines underneath represent marriage and connecting lines above represent siblings. Blue words are terms for older siblings, and red terms for younger. What's interesting is that if you follow along the younger aunt's and uncle's line, you will find identical terms for these relatives, as you will your older siblings (with the exception of кукка kuka, your mother's brother). Your mother's younger sister is аппа apa, and your older sister is аппа apa, and their husbands have similar terms. Your mother's younger sister is closer to you in age and may be like an older sister to you. While your older sister might take care of you, and thus be like an aunt. We find that this intergenerational pattern happens in the next generation too, when we look at children-in-law. Your younger sister's husband is your керу keru, as is your daughter's husband, reflected with your younger brother and your son. Clearly, your daughter is very different from your younger sister, but the men who marry the younger women in your life still have a similar relationship to you.
Along with gathering kinship terms, I'm also sitting down with quite a few family members and writing out our Chuvash family tree! I can't believe I have less than two months left, there's still so much to discover!