malapert

[underused]

malapert

(adj) boldly disrespectful; impudent
(n) an impudent person

It’s formed from the equally archaic apert, from Latin apertum, open, through French. The oldest English sense was “public, plain, unconcealed”, but this shifted over time until it came instead to mean outspoken and later insolent... the mal- prefix means “improperly, badly, wrongly” (as in maladjusted or malodorous), so creating malapert, of somebody improperly outspoken or inappropriately clever.
source

Malapert is listed everywhere as archaic. According to Michael Quinion at World Wide Words, it was "last used unselfconsciously in the seventeenth century."

Malapert, impudent, insolent--these are the words for channelling your inner English Headmaster.

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Would be lazy but for absence: click the link for 15 brilliant teacher comments taken from school reports of yore (as submitted to the Telegraph).