What is "priscian"

Latin Priscianus, name of a celebrated Roman grammarian (c.500-530); hence to break Priscian's head (1520s) "to violate rules of grammar" (Latin diminuere Prisciani caput). See Priscilla.

Priscianus Caesariensis , commonly known as Priscian ( or ), was a Latin grammarian and the author of the Institutes of Grammar which was the standard textbook for the study of Latin during the Middle Ages. It also provided the raw material for the field of speculative grammar.