Why do we use the term "in law"? Ya know Mother in law, Sister in law etc.
For example I'm fairly sure "the law" does not recognise me as an additional daughter of Dave's parents.
And if say I were to die that would not (as far as I know) make Dave my parents next of kin. That would probably be Fiona.
I like Dave's family and my family likes Dave so this is not a personal question. I'm just confused why we use a term which I'm pretty sure is inaccurate.
I think it must be an anachronism.