Green’s Dictionary of Slang

latro phr.

[‘Italianized’ version of later phr.]

(US campus) a farewell, goodbye.

[US]Eble Campus Sl. Fall.
[US]Eble Sl. and Sociability 100: The frequently used later is a shortening of something like see you later; it gives rise to latro and to the humorous rhyming expansion later, tater.