hardhead

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A shrewd, tough person.
• noun A stubborn, unmovable person.
• noun Any of several fishes having a bony head, especially the Atlantic croaker.

from The Century Dictionary.

• noun The name is also applied to many other fishes having hard heads: as in America to Chriodorus atherinoides of the family Hemiramphidæ, and Salmo gairdneri, a trout; in England to Myoxocephalus scorpius, a cottoid fish.
• noun Inthe Bahamas, a shrub of the spurge family, Phyllanthus Epiphyllanthus. Also called seaside laurel. See laurel, 3.
• noun Clash or collision of heads in contest.
• noun A small billon or copper coin of Scotland, officially known as the lion.
• noun The menhaden, Brevoortia tyrannus. See cut under Brevoortia.
• noun The California gray whale, Rhachianectes glaucus: so called by whalers because it has a habit of butting boats.
• noun The gray gurnard, Trigla gurnardus.
• noun The ruddy duck, Erismatura rubida, more fully called hard-headed dipper. Also hardtack, toughhead.
• noun A kind of commercial sponge
• noun The knapweed, Centaurea nigra: so called from its resemblance to the loggerhead, a ball of iron on a long handle. See knapweed.
• noun An alloy of iron, tin, and arsenic remaining on the bottom, after liquation, in the process of refining tin in the reverberatory furnace. It is nearly identical in composition with the dross removed from the surface during the operation.
• noun Alarge, smooth, rounded stone found especially in coarse gravel.

from the GNU version of the Collaborative International Dictionary of English.

• noun Clash or collision of heads in contest.
• noun Local, U. S. The menhaden. See Menhaden.
• noun Block's gurnard (Trigla gurnardus) of Europe.
• noun A California salmon; the steelhead.
• noun The gray whale.
• noun A coarse American commercial sponge (Spongia dura).

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One who is practical or hardheaded.
• noun A brown diving duck, Aythya australis, native to Australia.
• noun Any of various freshwater cyprinid fishes of the genus Mylopharodon, or of saltwater sciaenid (Sciaenidae) fishes.
• noun Any of several weeds in or formerly classified in the genus Centaurea, particularly russian knapweed (Acroptilon repens).
• noun metallurgy Residual ore that failed to melt during a smelting process.
• noun obsolete Clash or collision of heads in contest.