^ elevown, we’re mostly not talking about grammar per se here, but rather idioms—those little usage conventions that aren’t strictly logical but simply the way native speakers habitually use words. It’s not at all clear why in English trouser-like things became a plural while upper-body garments are singular—they just are.
It’s like in British (and elsewhere) English the short form of “mathematics” is “maths” while it’s “math” in the US, or how Brits say that someone is “in hospital” while US people say “in the hospital”—there’s no compelling grammatical reason, that’s just how it’s done.
My joke, which has now become exceedingly tedious, was based on the fact that whatever the fuck Hino had in that bag seemed to have lost any residual suggestion of “twoness” remaining in panties (I do note, tediously, that a G-string is also a singular noun).
Not that I’m a linguist: https://xkcd.com/2390/
last edited at Nov 26, 2020 10:00AM