Green’s Dictionary of Slang

groutnoll n.

also grout-nold, growtnol(l), grutnol
[SE grout, lit. coarse meal, taken as something large and rough + noll, head]

a fool.

[UK]Hollyband Treas. Fr. Tongue n.p.: Lourdault, a loute, a lob, a groutnoll [OED].
[UK]Beaumont & Fletcher The Knight of the Burning Pestle II iii: That same Dwarfe’s a pretty boy, but the Squire’s a grout-nole.
[UK]Dekker Gul’s Horne-Booke 5: Growtnowles and Moames will in swarmes fly buzzing about thee.
[UK]Urquhart (trans.) Gargantua and Pantagruel (1927) I Bk I 103: Noddie meacocks, blockish grutnols, doddi-pol-jolt-heads.
[UK]J. Cleveland Rustick Rampant 82: The other Growtnolls of the Neighbourhood [...] wait for them.
[UK]R. Nares Gloss. (1888) 390: growtnol, quasi growty noddle, i.e., dunce. A word, I suspect, coined by Decker, who is hardly sound authority for the usage of a word, unless supported by collateral examples.