So I was wondering: why do we call them a pair of knickers? A pair when it's only one item? A quick google and I have the answer - not from Wiki but from more reliable double-checked and compared sources I should add.
It wasn't until the end of the eighteenth century that women began to wear a form of drawers adapted from those worn by men, with legs gathered below the knee and lacing at the back around the waist. Prior to that women didn't wear anything on their nether regions.
Now the relevant bit of this is that these weren't so much crotchless panties as ... well, more like individual leggings. The crotch seam was open from front to back, of necessity I assume, as who'd want to struggle with laces when you had a pressing need to wee? A bit later they began to be called knickers from the knickerbocker trousers which were becoming fashionable. And this is where I am doing my 'Elementary, dear Watson' bit: I guess they were called a pair because to all intent and purposes they were in two pieces.
'Closed' drawers with a side-waist opening didn't appear until the end of the nineteenth century but now knickers were becoming prettier and more colourful - and made of silk - if you could afford them. And so it has continued over the years with more and more time and money being spent on designing and marketing tiny triangles of material.
And there you have it. Everything you need to know about knickers in one short blog post. Next time DIY brain surgery for beginners.