To break Priscian's head (in Latin, “Diminuere Prisciani
caput”). To violate the rules of grammar. Priscian was a great
grammarian of the fifth century, whose name is almost synonymous with
grammar.
“Priscian's head is often bruised without remorse.” —P. Thompson.
And held no sin so deeply red
As that of breaking Priscian's head.
Butler: Hudibras, Pt. ii. 2.
Priscillanists Followers of Priscillian, a Spaniard; an heretical
sect which sprang up in Spain in the fourth century. They were a branch
of the Manichæans.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
