nail-headed
/ˈneɪlˌhɛdɪd/adjective
1Of a character in a writing system or a stroke in painting: having the shape of a nail head. Compare nail head. Now rare.
2 Generally. Formed like a nail head; having a head like that of a nail.
3 Slang. Stupid; stubborn. rare.
Origin
Early 19th century. From nail + headed, after nail head.