Definition from Wiktionary, the free dictionary
Etymology 1 
mimsy (not comparable)
- (nonce word) A nonce word in Lewis Carroll's Jabberwocky combining the senses of "flimsy" and "miserable".
- All mimsy were the borogoves — Lewis Carroll, Jabberwocky
Etymology 2 
mimsy (plural mimsies)
- (vulgar, slang) The vagina.
- It seems plastic surgery for men is catching up in the lunacy stakes with the world of female plastic surgery, a place where you can fly to LA and get the shape of your vagina changed: what constitutes an appealingly shaped mimsy is something else to be filed under "unanswered questions", next to the one about who wants a huge pair of balls. — Alexis Petridis. "Nut Jobs?", The Guardian, 2008-08-30. Retrieved on 2008-10-08.