Questions about kinship terms (words for family members).

English has sparse terminology for family members compared to many languages. It was not always so— Old English had terms such as faþu for paternal aunt— but by Middle English, the limited modern set was established:

father, mother, uncle, aunt, brother, sister, husband, wife, cousin, son, daughter, nephew, niece.

Multi-generational relationships are signified with grand- or great-, and relationships through marriage may be signified by step- or -in-law. The more extended relations with whom you share grandparents, great-grandparents, and so on are all referred to as cousins, where the level of consanguinity is indicated numerically (e.g. third cousin twice removed).

All of the common terms except cousin are gendered, and in general, preferred to their gender-neutral words such as spouse or parent, which may be seen as impersonal.

The result of this paucity of kinship terms is that nearly every question asking is there a specific English word for relation X is answered with either no, there isn't or they would not be considered a relation, and they may not be well-received. In some languages, one's mother's sister, mother's brother's wife, father's sister, and father's brother's wife might all be referred to with different terms; some languages will draw further distinctions based on the age or gender of the speaker. In modern English, however, all of these women could be known as an aunt.

The reason why English lacks the richness of some other languages when it comes to kinship terminology, or why it adopted French terms for some but not other relationships, or the like are questions of anthropology rather than language. As they cannot be known with any more certainty than any other quirk of English, they are likely to be closed as off-topic or primarily opinion-based.