Why do digimon names end in 'mon'?
Digimon is like Pokemon where Pokemon is short for Pocket Monsters, that said Digimon is short for Digital Monsters
this is visiable in most logos for Digimon



Also in the first episode of the 4Kids dub of Digimon Adventure when the Digi-destined come back together after finding their Digimon Partners the Digimon says in unision (after Bukamon jumps off Joe's shoulder)

Bukamon: we are.....
All: Digimon! Digital Monsters