Origins
The word 'monitor' entered English in the 1540s from Latin 'monitor' (one who admonishes, an adviser, an overseer), an agent noun from 'monฤre' (to warn, to advise, to remind).โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ The Latin verb derives from PIE *men- (to think, to remember), specifically from its causative form *mon-eie- (to cause to think, to bring to someone's mind). In its earliest English use, a monitor was a senior pupil in a school appointed to keep order and supervise others โ a usage that survives in British schools to this day.
The Latin verb 'monฤre' generated a rich family of English words. 'Admonish' (from 'admonฤre,' to warn earnestly), 'premonition' (from 'praemonฤre,' to forewarn), and 'summon' (from 'submonฤre,' to advise secretly, to call up) all descend from it. Most surprisingly, so does 'monster' โ from Latin 'mลnstrum' (an omen, a portent, a supernatural sign), which was originally something that 'warned' or 'showed' the will of the gods. A monstrous birth was not just horrifying; it was a divine admonition. The related verb 'mลnstrฤre' (to show, to point out) gave English 'demonstrate,' 'muster,' and 'remonstrate.'
'Monument' is a close cousin: from Latin 'monumentum' (a memorial, a reminder), from 'monฤre.' A monument is literally something that makes you remember โ it admonishes you not to forget. Both 'monitor' and 'monument' are thus fundamentally about bringing something to mind.
Proto-Indo-European Roots
The broader PIE root *men- (to think) is one of the most prolific in the language. Through Latin 'mฤns' (mind), it gave 'mental,' 'mentality,' 'demented,' and 'mention.' Through Latin 'memor' (mindful), it gave 'memory,' 'remember,' 'memoir,' 'memorial,' 'memorize,' and 'commemorate.' Through Greek, it produced 'mania' (madness โ thinking gone wrong) and the '-mancy' suffix (divination โ inspired thinking). Through Germanic, it produced 'mind' itself (from Old English 'gemynd,' memory).
The technological sense of 'monitor' โ a display screen โ emerged in the mid-20th century. Early television production used 'monitor' for a screen that allowed directors to watch what the cameras were seeing, extending the sense of 'one who watches and checks.' When computer displays appeared, the term transferred naturally. The word has thus traveled from 'a person who advises' (1540s) to 'a warship that warns' (1862) to 'a screen that shows' (1950s) โ but in every case, the core meaning is the same: something that brings information to your attention, that causes you to be aware.
In modern usage, 'monitor' functions as both noun and verb. To 'monitor' something is to watch it systematically โ patients in hospitals, students in exams, network traffic, environmental conditions. The word has absorbed the full range of its Latin ancestor's meanings: warning, advising, watching, and reminding all at once.