To break Priscian's head; to write or speak false grammar. Priscian was a famous grammarian, who flourished at Constantinople in the year 525; and who was so devoted to his favourite study, that to speak false Latin in his company, was as disagreeable to him as to break his head.
PRISCIAN
Meaning of PRISCIAN in English
Slang English vocab. Английский сленговый словарь. 2012