grammatical number - Are there meta-plurals beyond "peoples"?

The plural of "person" is "people". The plural of "people" is "peoples". Person-people-peoples is the only sequence like this that I know of, but I'm looking for another.

(The equivalent question is, is there another plural noun which has become a singular countable collective noun?)

EDIT

For those of you that think that people is nothing but a collective noun (and not an irregular plural, like mice), I urge you to consider:

• Do you treat other collective nouns as plurals? One person, two people, but one star, two galaxy?



• Do you treat other plurals as collective nouns? You can certainly say "a galaxy of stars" but do you say "a mice of mouses"?

For those of you that think the customary plural of person is persons, try it on the next three, uh, persons you see: "Finish this sentence: 'one person, two _ ?' "

Answer

Fish, fish, fishes: one salmon, one fish, two, two fish; salmon is one fish, haddock another, so two fishes. Works with any noun where the singular and plural are irregularly identical, and the regular plural is used for categories or groups; in a more painfully literal fashion, this also applies to words where the plural has become singular in the common case: one agendum, two agenda; one agenda, two agendas.