I wonder how long the "pair of" phrasing can stick to things that were once a pair of items and got redesigned to be one thing, like trousers, or scissors (originally a pair of knives). My wife always says "scissor" singular, which I thought was weird but now think is the just way the language will go eventually.
How long can we stick with "hang up the phone" and "off the hook" now there is no separate handset and no hook or base? And finaly, why is it "a pair of underpants" when that could never have been two garments?
Singular "pant" has recently-ish become accepted fashion industry jargon: "Our spring collection includes a khaki pant and a capri pant". I've started to see it creep from there into everyday language.
This might stem from noncount noun rules rather than any particular trend for the word "pants".
Typical example is the word _water_. It is noncount except when talking about types of water. E.g., this year we introduced a vitamin water and an energy water to our line of beverages. By extension, you can pluralize it: we introduced two new waters this year.
I don't disagree that pants might be slowly becoming countable, just noting that the particular verbiage of "a capri pant" or whatever can be produced using the usual rules.
How long can we stick with "hang up the phone" and "off the hook" now there is no separate handset and no hook or base? And finaly, why is it "a pair of underpants" when that could never have been two garments?