some of that confusion comes from the what is "paired"...for instance, "jeans" has a plural connotation, even if "pair" refers to the ancient practice of two separate fabric leg coverings paired together for one garment, like "hose" or "pants" or "trousers". If the word "knickers" was used instead of "underwear" (the latter having no final "s") it seems easier.
And clothing is not all that has that weird etymology---there is also, at least, the case of "scissors" and "shears" which were once separate blades, then joined into a pair for easiest use.
Can you tell i'm bored?
Will: They don't give out awards for helping people be gay... unless you count the Tonys.
"I guarantee that we'll have tough
times. I guarantee that at some point
one or both of us will want to get out.
But I also guarantee that if I don't
ask you to be mine, I'll regret it for
the rest of my life..."