def. An especially unattractive member of an otherwise good-looking group of socializing females.

Addendum: Also sometimes known as the "Fat Friend," one will observe that the Friendasaurus is sober and apparently PMSing, which aids in her dual roles of the outing; being the DD for the group, and as the Grandmaster Cockblocker, foiling any attempts for an eventual sexual encounter with one of the more attractive ladies of the group.
Guy1: "Dude, 2 O'clock, the redhead, she's STUPID hot!"

Guy2: "Yeah, but you see the nasty chick dancing next to her? She's a major Friendasaurus; I just saw her cockblock that guy in the green shirt."
by nutman November 23, 2004
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There is always an obligatory "fat" friend in any group of hot girls... the Friendasaurus!
Look at the bloody Friendasaurus in that group!!
by imnotasthinkasyoudrunkiam September 11, 2008
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When an attractive girl has a surprisingly unattractive friend that always hangs around providing a constant living cock block for all men trying to make a play.
I was about to spit some game on this chick but her Friendasaurus was always on the prowl.
by the brown bear August 15, 2008
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