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Simply a variation on the classic MILF that is well known. This is referring to a "Sister-In-Law-I'd-L ike-to-Fuck."

Those boots my Sister-in-law was wearing at the reception seriously made her look like a SILILF.
by Imogen Mann December 13, 2007

Words related to SILILF

in law milf mililf sister sister-in-law