It's a loose Japanese Translation, as Critical says. Translated literally, Raging Brachydios' name is something like "Sudden Explosion Brachydios".Y-yeah that's right, I totally knew that. Hehe...
Considering the nature of his drop names, it's no wonder his nickname is related to nuclear fission terminology.
If only there was a way to have map/level updates and harder battles *sigh*
MH5 better hurry up, although doubt it will be on the 3ds (probably might be on the New 3ds).