Cookie vs biscuit, vacation vs holiday, gasoline vs petrol, etc, etc.

Cookie and biscuit are two different things. Which two depends on country, but still two different things

The point is what in the Uk is called a biscuit in the US is called a cookie. Similarly for the other pairings.

Do ginger cats make the same biscuits as orange cats?

Though, https://www.reddit.com/r/catsinpants/ works for both forms of English.

This sense of biscuit persisted in US English for a long time. The National Biscuit Company (makers of oreos and fig newtons) only changed its name to Nabisco in 1931. The Kennedy Biscuit Company was subsumed by the New York Biscuit Company which merged with the American Biscuit Company to form the National Biscuit Company in 1898. Closes Wikipedia

Cookies in the UK are a subset of biscuits, but not all biscuits are cookies. Do you not have any other types of biscuits (using the UK term) in the US?

No, a biscuit in the US almost universally narrowly refers to a flaky, buttery, savory pastry typically eaten at breakfast, either with a sweet jam or a savory sausage gravy.

“Biscuit” is not a category of foods in the US, while “cookie” is absolutely a category of desert with many different kinds.

If you ask for a biscuit here, you’ll get the same thing every time. If you ask for a cookie, you’ll be asked “what kind?”

No. A biscuit is something entirely different in the US. We just have many types of cookies.

FWIW, I believe petroleum is a synonym for crude oil. If you put it in your cars fuel tank, you'll have a bad time. Gasoline is made from petrolium.

I'm pretty sure petrol means gasoline not petroleum.

Petrol is technically just short for petroleum, which is latin for "rock oil"

Gasoline is from gas + plus the chemical suffix "ol" short for the latin "oleum", and "ine" meaning "made of".

But the etymology of a word doesn't prove that someone is using that word wrong, or people on both sides of the pond would have to start baking our biscuits a second time.

petrol !== petroleum

the confusion is solely in your reading comprehension skills and not in the GP's use of the words