In computer acronym sil means sister in-law.
I've always wondered What’s the computer acronym for son in law?
I've tried for ever-so-long to find out, but no one seems to know.
So, I thought I'd ask it here and see if any one knows.

Thanks so much, I look forward to finding out what it is.

Oo, that's such a good question. I decided to look it up to see what people are using. One forum group listed acronyms and whilst keeping Sister-in-law as SIL, then assigned SNIL to Son-in-law.

However, the Ancestor Search by US Census abbreviations has really covered all the bases for relative acronyms. For example:

Son-in-law as Sl
Sister-in-law as Sil
Step Son-in-law as Ssl
Step Sister-in-law as Ssil

Thank you thank you thank you You have solved a mystery that has bugged me for years. I'm tickled pink.

You are the best!

It was truly an interesting question you posed.