E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Priscians Head.
To break Priscians head (in Latin, Diminure Prisciani caput). To violate the rules of grammar. Priscian was a great grammarian of the fifth century, whose name is almost synonymous with grammar.
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Priscians head is often bruised without remorse.P. Thompson.