(not to be confused with the comic book character published by Marvel Comics)
(also not to be confused with the 1974 movie, Juggernaut, starring, of all people, Richard Harris, Omar Sharif, and Anthony Hopkins)
(though both of these are based on definition #1)
1. any large, overpowering, destructive force or object
2. anything requiring blind devotion or cruel sacrifice
Now, I knew definition #1 from all those steampunk novels being published lately, but it was definition #2 I needed and was surprised by.
Whenever I think of a juggernaut, I think of this image of a Clanker (known as the Cyklop Stormwalker) from Scott Westerfeld's book Leviathan (amazing book! read about it here!), drawn by incredible artist Keith Thompson.