Venting

Dame Venting ran the school that Sam Vimes attended for nine whole months, during which time he rose to the exalted position of Blackboard Monitor. This was rife with heady strutting power when he was six, but counted against him inordinately when he dealt with the Dwarfs later in life...

The name may be only a description of Dame Slightly when gin and unruly urchins overcame her normally tolerant disposition. (The possibility of a data-entry error in The Author's character file may have to be considered as well.)