I am using the word spectre for both of its meanings. "a ghost" or at least something hidden, and "something widely feared as a unpleasant or dangerous occurrence."
I'm racking my brains for another noun I can use; something which is also dangerous but in a more straight-forward and up-front way.
The reason is that I'm attempting to create names which people in a story may give to deadly mechanical creations. I have three different "types". The first is sneaky like a ghost but deadly(spectre) and human-sized.
The second is rather large (house-sized) and loud: you can see it coming but you can't stop it. "Juggernaut" would be the perfect word for it, but I'm debating whether that word is kind of cliche, so it may also be something along the lines of Behemoth or Collossus.
The third is the one I'm having trouble naming, probably because it has somewhat of an identity crisis. It is a mix between the first two, with the speed and slightly larger size than the spectre, but the up-front power and unstoppable force of the Juggernaut.