My sibling's husband is my brother-in-law.
My sibling's wife is my sister-in-law.
My spouse's sister is my sister-in-law. I also refer to her husband as my brother-in-law.
My spouse's brother is my brother-in-law. I also refer to his wife as my sister-in-law.
Instead of making this forum your first port of call for definitions, Polyester, you'll get quicker answers if you avail yourself of the advantages of free online dictionaries.
Click here and bookmark the site for future reference.
If you have a question about the English language and would like to ask one of our many English teachers and language experts, please click the button below to let us know: