ULTIMO
ultimo, ult
(adjective) in or of the month preceding the present one; “your letter received on the 29th ult”
Source: WordNet® 3.1
Etymology 1
Adjective
ultimo (not comparable)
(obsolete) On the last day (of a specified month).
Adverb
ultimo (not comparable)
Of last month.
Etymology 2
Noun
ultimo (plural not attested)
(obsolete, rare) = ultimum
Source: Wiktionary
Ul"ti*mo. Etym: [L. ultimo (mense) in the last month.]
Definition: In the month immediately preceding the present; as, on the 1st
ultimo; -- usually abbreviated to ult. Cf. Proximo.
Source: Webster’s Unabridged Dictionary 1913 Edition