system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we use "pair" to indicate singular things?

For example, a pair of jeans, or a pair of underwear. It's a single clothing item, why do we call it a pair? Is there any situation on which we use this for anything other than clothing?
gpt
Pants were originally two things - actually a pair.  "Pantaloons" were put on one leg at a time.  Underwear, shorts etc. are all derivative things and have inherited their pluralness from their full-legged friend.