Green’s Dictionary of Slang

1. an intellectual, anyone considered to work with brain rather than brawn.

1907		O. Johnson Sat. Eve. Post 16 Nov. 9/1: His genius lived in the nicknames of the Egghead [...] and the Coffee Cooler.
1911		S.F. Call 21 May 6/1: The Triumphant Egghead had discovered the resemblance.
1918		C. Sandburg Letter (deposited in Toledo-Lucas County Public Library, Toledo, OH) n.p.: Dear N. D.‘[...] Egg heads’ is the slang here for editorial writers.
1953		R. Chandler Long Good-Bye 289: I told him I didn’t think it would do Springer any harm. ‘Only with the eggheads,’ Lonnie Morgan said, ‘and they already had his number.’.
1959		E. De Roo Young Wolves 20: If those eggheads give you any trouble let me know.
1962		S. Longstreet Flesh Peddlers (1964) 158: Mon, yo’ is a egghead.
1969		‘Iceberg Slim’ Pimp 138: She sounds like an egghead.
1979		Fantastic Four Annual 16: Even a non-egghead like me can figure out what’s happening.
1989		T. Blacker Fixx 216: Some group of professional busybodying eggheads.
1996		P. Beatty White Boy Shuffle 157: The ersatz egghead lived in Cheviot Heights.
1999		Guardian Weekend 5 June 34: She [...] sent him to a Farm Street egghead for the final brush-up.
2000		W.T. Vollmann Royal Family 5490: I’d rather not quote Gibbon. The guy was an egghead.
2005		K. Huff A Steady Rain I i: You are the egghead. I am the walrus.
2014		J. Porter ‘Good Luck in Puerto del Oro’ in ThugLit July [ebook] Perched on the bed was the egghead I'd been sent to find.

2. a pretentiously intellectual type.

1968		I. Reed Free-Lance Pallbearers 129: You gotta watch these eggheads.
1970		H.E. Bates A Little of What You Fancy (1985) 452: On one occasion [...] she had thrown over the fence, like a verbal hand grenade, the phrase ‘red egghead!’.
1998		P. Doyle (con. late 1950s) Amaze Your Friends (2019) 65: ‘A wash-up egghead, beatnik, jazz-dag’.