I'm sure it's the same word association that powered Zyuranger, Dairanger, Kakuranger, etc.; ditto with Dynaman, Fiveman, Jetman, etc.
Incidentally, I just watched the first episode of Kyoryuuger, and had more fun with it than I thought I would (being a fan of the more paramilitary / vehicle sentai years). A particular note was how this team, at least at the outset, WANTS to maintain secret identities, even to each other. I'm sure I'll catch the odd episode going forward but I think the kids'll love it.