I got the part about what I call underpants being “pants” or maybe “knickers”, but then what do you call what I would call pants:
Trousers
Trousers.
Well, nothing to see here folks, we can all go home. Thread’s over.
I dropped my trousers at the dry cleaner’s last week.
I’m glad I wasn’t there.
Were you wearing pants?
Follow up question:
If pantyhose in the US are tights in the UK,
what are US tights in the UK?
I just now realized where “trou” in the phrase “dropped trou” came from.
Tights are tights and pantyhose are stockings. That mirrors the US, though, because I don’t know anyone who calls them pantyhose (::shudder:
anymore.
“Britches” for “pants”?
Separated by a common language, indeed.
No no, breeches are what horse riders who wear long boots wear, or Mr Darcy.
My tasteless mother used to refer to harem pants (the baggy ones with cinched-in ankles) as “dysentery britches”.
Weren’t those called “jodhpurs”? My relatives in the South still use the word “britches” but I think that’s for underwear (as in “shit yer britches”). I’m just being a pest, here. 
Please explain “Mr. Darcy” reference?
Mr. Darcy (beloved breeches-wearing hero of Jane Austen’s Pride and Prejudice)
“Britches” is also still used idiomatically (by those of a certain age) in “too big for your britches”, to mean cocky.
My Mommy called me that just last week 
.
Thanks for the Darcy info, SpoilerVirgin. I’m so illitrit.
If this thread goes on for much longer, someone is going to get kilt.
“Trouser” can be used as a verb to mean “secrete away”. Usually money, and usually nefariously. eg
I hear Simon Cowell trousered five grand from Susan Boyle for getting her on Britain’s Got Talent*
*Allegedly