The New Oxford American Dictionary has the following note.
For complex historical reasons, prove developed two past participles: proved and proven. Both are correct and can be used more or less interchangeably: this hasn't been proved yet; this hasn't been proven yet. Proven is the more common form when used as an adjective before the noun it modifies: a proven talent (not a proved talent). Otherwise, the choice between proved and proven is not a matter of correctness, but usually of sound and rhythm—and often, consequently, a matter of familiarity, as in the legal idiom innocent until proven guilty.
Cardinalis means "that upon which a door hinges, pivotal" in Latin, from cardo, "hinge, pivot". From this it acquired its secondary meaning, "important, principal", which it still has in English (e.g. a cardinal sin). Its third meaning is derived from this: a cardinal number is a "principal" number, i.e. one that simply says how many objects there are.
That'll be one pound.
Two billion people might die.
Ordinalis means "in order of succession, of an order". It comes from ordo, "order, rank". An ordinal number is an adjective that denotes what place an object has in a certain order. The names of the ordinal numbers are usually derived from the cardinal numbers by adding -th.
That is my second victory.
This is the tenth time she's dumped me.
While a cardinal number refers to several objects ("three apples"), an ordinal number refers to only one of those ("the third apple"). An ordinal number is hence dependent on the notion of a cardinal number: there can't be a third apple unless there are at least three apples. By contrast, there can be three apples without one being the third, if they are just not arranged in any particular order.
The Romans used these terms the same way. They also had distributive numbers, which indicated "every third apple", or apples "in triads", "three each".
Best Answer
An excert from here:
This is an AE perspective but, I would say that trousers and pants are synonyms. With both being any outer garment that covers both legs separately and goes from waist to ankles. Technically slacks is also a synonym, but the informal definition I most frequently hear is that slacks = dress pants. I.E. Pants that you might wear if you were trying to look nice.