Definition of "hardhead"

One who is practical or hardheaded.  examples

A brown diving duck, Aythya australis, native to Australia.  examples

Any of certain saltwater sciaenid (Sciaenidae) fishes.  examples

Mylopharodon conocephalus of fresh waters in California.  examples

Any of several weeds in or formerly classified in the genus Centaurea, particularly Russian knapweed (Acroptilon repens).  examples

(metallurgy) Residual ore that failed to melt during a smelting process.  examples

(obsolete) Clash or collision of heads in contest.  quotations

(historical) A Scottish billon coin circulated in the reigns of Mary and James VI.