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20.
Basically, you have normal thighs, then they get fat (tier 1). But when they get like even fatter, you get another level of fat like a hill of fat(tier 2), which is loose off the other fat so when a thunder thigh is being walked besides the legs (tier 1) rubbing against eachother they (tier 2) hit eachother making a noise, hence thunder coming into the expression, most likely to because of alliteration for a dramatic, comedic affect. This sound can have a brighter tone and richer feel if accentuated with bumpy cellulite
Damn, those thunder thigs are so massive it looks like shes got a second arse

It's like someones stuck balloons in those thunder tighs

No, no....come on, this cant be real, that girls got thunder thighs ripping out like the hulk
by F-Laboyrie May 31, 2007
 
1.
Of a woman, large, broad hips and thighs. One of the most tasteful images possible is a woman of such build in a bikini.
Yeah that's right. What the above definition SHOULD SAY. Goddamn anti-fat bastard!
by IcyHaku December 01, 2004
 
2.
"THUNDER THIGHS" are a fat girls thighs that are so humoungous, big & fat that they clap together when they walk. This produces a loud noise which goes like "SLAP, SLAP, SLAP" , hence the "thunder" part of the word.
Look at that girls thunder thighs!
by Emily December 28, 2004
 
3.
a pair of big ass thighs.
Her thunder thighs couldn't even fit in her jeans.
by Kenny October 27, 2004
 
4.
Thick thighs on a curvy(not fat) lady. usually a girl with thunder thighs has a Nice A**!
guy1; dayumm shawty got sum thunder thighs
guy2;FEREALLL HOMIE,she got a nice ass too.
by NAWWMEAN July 11, 2009
 
5.
A pejorative term for a person with large thighs, alluding to the sound of thighs hitting against each other.
Person 1: Whoa, check out thunder thighs over there. EARTHQUAKE!

Person 2: Actually, I think thunder thighs and wide hips are kinda hot.
by D-S February 19, 2006
 
6.
The thighs of a curvy voluptuous woman, famous in the 70s and early 80s period which adds a seductive, sensual appeal to the whole persona of the woman; unlike a skinny, lean pair of legs so much in fashion and so desired now.
Wow! Check out the thunderthighs on that woman, makes me want to make sweet love to her all night long.
by Im ur stitch February 28, 2013
 
7.
n. huge thighs
Mika Nakashima has thunder thighs!!!
by the donut April 24, 2003