It's a common vagary of the English language that pants—or trousers, slacks, khakis, shorts—is always presented as a plural. It's never pant, but rather a pair of pants. ... A shirt is just pants for your top half, and that's a singular object, even though there are holes for each of your independent arms in which to go.

Is slacks singular or plural?

Plural form of slack. The word slacks is defined as a pair of pants. An example of slacks is the nice pair of pants you put on to go to work.

Why are pants plural but not shirt?

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.