Proper noun
(geography) Synonym of Mexico (as opposed to New Mexico).
(geography, history) The land of Mexico under Aztec rule; ancient Mexico.
Source: en.wiktionary.orgAnd I dream in the morning that she brings me water And I dream in the evening that she brings me wine Just a poor man's daughter from Puerta Piñasco South of the border, in old Mexico. Hoyt Axton