Hardheads

noun

1. One who is practical or hardheaded.
2. A brown diving duck, Aythya australis, native to Australia.
3. Any of various freshwater cyprinid fishes of the genus Mylopharodon, or of saltwater sciaenid (Sciaenidae) fishes.
4. Any of several weeds in or formerly classified in the genus Centaurea, particularly Russian knapweed (Acroptilon repens).
5. Residual ore that failed to melt during a smelting process.