Guide of the Desert by Gustave Aimard — Read

Montonero, the feminine of which is montonera, is essentially an American word, although its root is undoubtedly Spanish. It signifies, literally, a heap, a mass, a collection. Taken in the bad acceptation of the word, a montonera means a gathering of men of the sack and cord -- of bandits without faith or law -- of highway robbers.

But this is not the meaning which was at first given to the word. They understood by montonera, a cuadrilla -- a guerilla composed of banished politicians -- of insurgents who made war as partisans at their own risk and peril, but who were brave and honest.