[jonhohle]

Fish is the plural of fish. Sheep is the plural of sheep. Trousers is the plural of trousers. And math is the plural of math.

[OJFord]

I have to object to trousers - that's because it's already plural - 'a pair of trousers'; we just don't use the singular much, but trouser leg, trouser press.

[jjgreen]

Indeed, and in the fashion world: "This year, kippers will be worn outside the trouser"

[denton-scratch]

And yet we have a "trouser press". Nobody refers to a "trousers press". Also "trouser suit".

I love the irregularity of English.

[marcus_holmes]

Fish is the plural of fish only if all the fish are of the same species. If it's a mixed group of fish then the plural is fishes [0].

Same with maths - if you only have one type of mathematics then math would make sense. But there are many types of mathematics, so we call it maths.

[0] https://www.grammarly.com/blog/fish-fishes/

[happymellon]

Luckily, there is no such thing as a fish.

[thr-nrg]

Fish is not the contraction of fishematics though.