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1.
One step above "Cougar" in the scale of women. Pussy so old its fossilized.
a.k.a. Rapidly aging, Botox-addict and ex-supermodel Janice Dickinson.

" Man, what a gynosaur...I'd probably screw her, just gotta remember to blow the dust off first. "
by the Den of Iniquity October 06, 2006
 
2.
a gynecologist dinosaur
Dr. Lickalottapuss, do you suppose there were many gynosaurs helping deliver babies in the Jurassic period?
by dookeyboy November 21, 2010
 
3.
A term used to describe either a highly horrendous looking or obese woman who relentlessly pursues the male sex. In other words, a fat or ugly chick who chases unwilling men.
Dude, that gynosaur totally tried to jump Jimmy the other day!
by Not One OR July 06, 2011
 
4.
Pronounced:: Guy-no-sore-

Definition:: A woman who is well past her prime (usually mid forties and up, though age does not have to be the determining factor) yet is still actively seeking sexual relationships with men who are much younger or well out of her league.

Alternatively a younger women that looks much older, or appears to have been around the block more than her share of times can be referred to as a gynosaur.

Whereas the being, or sleeping with a cougar has become more acceptable in recent years, the same cannot be said of a gynosaur. Gynosaurs are most often cougars that never learned when to stop.
Guy 1: Dude did you see that milf over there?

Guy 2: No, where?
Guy 1: She's standing right over there next to those two gynosaurs.

or

Guy 1: Hey did I see you mom at the bar last night?
Guy 2: Yeah she was celebrating her 50th birthday with some friends.
Guy 1: Dude she kept trying to hit on me, thats gross she's a total gynosaur.
by Eyesmokepcp December 26, 2009
 
5.
A lesbian who can't get enough of eating pussy or being eaten out. Essentially, a cunnilingus addict. Also into finger-fucking.
Do you suppose Britney and Lindsay are gynosaurs?
by Steely Dan Fan May 25, 2007