From The Collaborative International Dictionary of English v.0.48 [gcide]:
Hellbender \Hell"bend`er\, n. (Zool.)
A large North American aquatic salamander ({Protonopsis
horrida} or Menopoma Alleghaniensis). It is very voracious
and very tenacious of life. Also called alligator, and
water dog.
[1913 Webster]