Thought this up in Physics and thought I would share, goes along the lines of stuff like from World War Two: Able, Backer, Charlie, Dog, Easy, Fox, George etc.
Aboleth, Beholder, Chimera, Dragon, Elemental, Fireball, Gargoyle, Hydra, Imp, Janni, Kobold, Lich, Minotaur, Neogi, Ogre, Pegasus...