grouthead, n. — Green’s Dictionary of Slang

grouthead n.

[SE grout, lit. coarse meal, taken as something large and rough and/or SAmE grout, to grumble + -head sfx (1)]

a fool, a simpleton.

c.1510		Colyn Blowbols Testament line 371: Sybour Groutehed a man full discrette, Whiche wil be dronke with myghti wynes swete.
1593		‘Philip Foulface’ Bacchus’ Bountie in Harleian Misc. II (1809) 307: His name was Gotfrey Grouthead; and with him he brought a wallet full of woodcocks’ heads.
1599		Nashe Praise of the Red Herring 39: Those Turbanto grout-heads, that hang all men by the throates on Iron hookes.
1630		J. Taylor ‘Sir Gregory Nonsense’ in Works (1869) II 3: There you may see many a greedy grout-head, / Without wit, or sence, almost without-head.
1841		Staffs Gaz. 20 May 4/6: Yet trust not Hob Grouthead for sleeping too long.