Is it farther or further?
"slow-witted person," 1867, American English colloquial, shortened from lunkhead (1852), possibly an altered form of lump (n.) + head (n.)
: four books about a lunk hero Carlo Reinhart
A stupid person; lunkhead: Lunks, Hunks and Arkifacts/ a character whom Tristan describes as ''a big lunk'' (1867+)
A stupid person; boob, dope, lunk: a bulky, duckfooted lunkhead/ Tenors have been traditionally stereotyped as vain lunkheads (1852+)