Green’s Dictionary of Slang

(US) a $100 bill.

2001		T. Egan Down Tick 65: The “6” was a flat two-hundo with another $125 added on to the bill for course materials.
2004		J.A. Juarez Brotherhood of Corruption 227: ‘Can you give me change for this hundo?’.
2014		C. Eble UNC-CH Campus Sl. Spring 2014 8: HUNJ PIECE — /h?n?/ one hundred dollar bill. Also HUNDO.