monitor [E16th] Today’s familiar uses of monitor, for a computer or TV screen or for checking the progress or quality of something, date only from the mid 20th century. A much earlier sense was ‘a reminder or warning’, reflecting its origin in Latin monere ‘to warn’, the source also of admonish [ME], monster [LME], and monument [ME]. A monitor lizard is a large tropical lizard, in Australia also called a goanna (a M19th corruption of *iguana), whose name derives from the way its reactions can warn people of the presence of a venomous creature. In schools from the 16th century a monitor was a pupil with responsibility for supervising and disciplining other pupils, who in the past might have also done some teaching.