We wear a shirt, a jacket but a pair of pants.
Why is pants plural?
The site has an entire page on this issue. Here's a brief snippet.
Before the days of modern tailoring, such garments, whether underwear or outerwear, were indeed made in two parts, one for each leg. The pieces were put on each leg separately and then wrapped and tied or belted at the waist (just like cowboys’ chaps). The plural usage persisted out of habit even after the garments had become physically one piece. However, a shirt was a single piece of cloth, so it was always singular.
Apparently in the past they were two tube weakly linked, think to current tights. Hence the plural form.
It actually makes perfect sense. Think of these examples. "The clown wore a pair of pants where one pant was red and the other pant green". Also, "The amputee wore his pants with one pant tied up and the other pant covering his good leg". The proper use of the singular and plural is used to make the meaning clear. Or if you look at panties as a whole with two openings or two short upper leg coverings we use the plural, however, if we only refer to the single toursal opening we say "panty waist", especially when referring to a male who is less masculine or who acts cowardly. And by the way "sleeves" is upper body equivalent of pants. "The shirt has short sleeves". "He wore short sleeves". In both these examples we used sleeves as a noun. When we use it as an adjective of a singular noun, we use the singular, ". . . short-sleeve shirt".
It's referring to the components that make up the whole. A pair of pants consists of two pants. Much like a pair of glasses (usually) has two pieces of glass.
I think it just like the "shoes". You cannot have one "shoe" as well as one "part" of the pants.
Thank you for your interest in this question.
Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
Would you like to answer one of these unanswered questions instead?