For two millennia it was a "little hill" - the meaning of kleitoris, its root word in Greek.
Dr O'Connell's finding has forced a rewriting of medical texts
But an Australian urologist, Dr Helen O'Connell, has revealed that the clitoris is shaped more like a mountain than a hill.
Her work is forcing a re-write of anatomy books and a rethink among medical professionals.
The findings could also have repercussions for women coping with continence problems.
The clitoris rivals the penis in size.
"The vaginal wall is, in fact, the clitoris," said Dr O'Connell, who is based in Melbourne.
"If you lift the skin off the vagina on the side walls, you get the bulbs of the clitoris - triangular, crescental masses of erectile tissue."
The idea had been that the clitoris is more than just its glans - the "little hill" but Dr O'Connell discovered the mistake 17 years ago.
Frustrated that she kept failing a medical exam, she went back to the anatomy books for answers. She discovered they were wrong.
"They left it out," she said. "It boils down to rivalry between the sexes: the idea that one sex is sexual and the other reproductive.
"The truth is that both are sexual and both are reproductive."
The Australian Doctor's Fund - a medical policy think tank - is demanding more time for anatomy in Australian medical schools.
The teaching of basic sciences - including biochemistry, pathology and anatomy - is so inadequate, it says, it has made a submission to the Australian federal government, demanding an overhaul of doctors' training.
But Dr O'Connell believes the quality of training is just as important as the quantity.
"Pelvic anatomy is not that easy to display or have interpreted," she said.
"Most people struggle with dissection-based images. They are quite confronting."
Dr O'Connell prefers to work with magnetic resonance images (MRI) to define the true size and shape of the clitoris.
By imaging the pelvises of healthy humans - rather than dissecting dead ones - she has found that the live clitoris is even larger than she first thought.
"There's nothing quite like the shape of a clitoris," she said.
"The glans are dense with nerve endings and receptors - all the vibration and sensation is there."
The bulk of it is shaped like a pyramid, she said.
Its base forms the external genitalia or vulva; its triangular "walls" are wrapped around the urine-carrying tube known as the urethra and the vagina.
When aroused, the whole structure becomes engorged.
"Helen has gone to significant effort to confirm what we suspected," said Dr Margaret Davy, director of gynaecological oncology at the Royal Adelaide Hospital in South Australia.
"The original anatomists weren't interested in the clitoris. The penis was much more interesting.
"It was bigger and you didn't have to wear your spectacles to see it."
Dr O'Connell's latest scientific paper investigates whether a medical device treating stress incontinence could interfere with clitoral function.
There are repercussions, also, for women who have undergone female genital mutilation.
Removing the glans of the clitoris does not mean the whole structure is lost, since it reaches deep into the body.
The greatest impact, however, is likely to be on the sex lives of couples who use the anatomy to their advantage.
"The sex industry has known about this for some time," said Fiona Patten from the Eros Association, Australia's adult retail and entertainment industry body.
"You only have to look at the adult products on the market to see that they are not designed to find some tiny button at the top of the vagina.
"They're designed to stimulate a much larger area."