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Wifes sister, brothers sister.

also see SILF - Sister In Law I'd Fuck
"Man, Your SIL is Smokin hot"
by EVP January 22, 2008
An abbreviation for Strong Independent Lady.

a) Term used to protect a woman from being called a derogatory name.

b) Term used as code for a mean, mean, witchy, shrew of a woman
You: "Man, my boss is such a $%^&!"

Them: "No she is just a Strong and Independent Lady and you just can't handle that."

You: "Yes! thanks for High Roading me there. You're a SIL too!"

Them: "Thanks!"
by Grymm Deth September 30, 2009
something that is described as being cute, little, lovable, italian, gorgeous, and so on. Used when describing a person you feel affection towards.
Myles is such a sil! or Love you sil.
by lil em March 10, 2008
Shit Intensity Level; From 1 to 10, 1 being a pleasureful dump, 10 being hot-tamale diarrhea.
Guy: Man dude, I had a SIL of 10 just now, shouldn't have had that taco bell last night...

Guy's Friend: Dang dude! That must have hurt!
by hudzell September 29, 2014
Should I Leave
This bitch is annoying SIL?
by Zaddie March 01, 2014
One who is silly, or could be described as such.
Man, that Katie Knutson girl is a major sil! She liked the movie About a Boy and thinks Conan is funny!
by LP_hoss July 10, 2008
Shortened version of School of Information and Library Science.
The SILS program at UNC is supposed to be really excellent.
by Yo386 September 27, 2010