What does "hardhead" mean?

Hardhead: (Zoöl.) (a) The menhaden. See Menhaden. [Local, U.S.] (b) Block's gurnard (Trigla gurnardus) of Europe. (c) A California salmon; the steelhead. (d) The gray whale. See Gray whale, under Gray. (e) A coarse American commercial sponge (Spongia dura).

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