Italian word mostro comes from Latin moneo (I remind. I warn, advise.)

Detailed word origin of mostro

Dictionary entry	Language	Definition
moneo	Latin (lat)	I remind. I warn, advise.
monstrum	Latin (lat)	(figuratively) a thing that evokes fear and wonder. (metonymically) a monster, monstrosity, whether in size or character. A divine omen indicating misfortune, an evil omen, portent.
monstro	Italian (ita)
mostro	Italian (ita)	Monster.

Words with the same origin as mostro