ultimo

Etymology 1

First attested in 1582; from Latin ultimō (elliptically for ultimō diē or ultimō mēnse), masculine ablative singular form of ultimus (“last”); cognate with Dutch ultimo, the German ultimo, the Swedish ultimo, etc.

adj

1. (obsolete) On the last day (of a specified month).

adv

1. Of last month.
   I receivd your favour of the 18th Ultimo in due time & beg pardon for not having answerd it before. 20 November 1771, Alexander Hamilton, “From Alexander Hamilton to Fraser, Grant and Baillie, 20 November 1771”, in Harold C. Syrett, editor, The Papers of Alexander Hamilton, volumes 1, 1768–1778, New York: Columbia University Press, published 1962, →LCCN, →OCLC, page 15

Etymology 2

First attested in 1622; from either the Italian ultimo, or the Portuguese último, or the Spanish ultimo; compare ultime.

noun

1. (obsolete, rare) = The ultimum; the final, ultimate point of a sequence.