I went to Internet looking for "mensiverary" and found a couple sites! Dated June 2000 I had to copy and paste the URL to make it work. Not sure why.

http://andrea.editthispage.com/2000/07/25

Anniversary Um... anniversary does not seem the right word, since it comes from "annum", which is latin
and means year. At least that's what I believe. (Yes, I did take Latin at school - for six years!)
So maybe I should call it "mensiversary" instead.