Allen and Greenough's New Latin Grammar for Schools and Colleges
J. B. Greenough, G. L. Kittredge, A. A. Howard, Benj. L. D'Ooge, Ed.

[*] a. For the declension of ūnus , see § 113. It often has the meaning of same or only. The plural is used in this sense; but also, as a simple numeral, to agree with a plural noun of a singular meaning: as, ūna castra, one camp (cf. § 137. b). The plural occurs also in the phrase ūnī et alterī, one party and the other (the ones and the others).

[*] b. Duo,¹ two, and trēs, three, are thus declined:—

[*] Note.-- Ambō, both, is declined like duo .

[*] c. The hundreds, up to 1000, are adjectives of the First and Second Declensions, and are regularly declined like the plural of bonus.

[*] d. Mīlle, a thousand, is in the singular an indeclinable adjective:—

1. mīlle modīs, in a thousand ways.
2. cum mīlle hominibus, with a thousand men.
3. “ mīlle trahēns variōs colōrēs ” (Aen. 4.701) , drawing out a thousand various colors.

In the plural it is used as a neuter noun, and is declined like the plural of sedīle (§ 69): mīlia , mīlium , mīlibus , etc.

[*] Note.--The singular mīlle is sometimes found as a noun in the nominative and accusative: as, mīlle hominum mīsit, he sent a thousand (of) men; in the other cases rarely, except in connection with the same case of mīlia : as, cum octō mīlibus peditum , mīlle equitum, with eight thousand foot and a thousand horse.

[*] e. The ordinals are adjectives of the First and Second Declensions, and are regularly declined like bonus.