mon

The root mon comes from Latin monēre, "to warn, advise, remind." Its core idea is to put something into someone's mind so they don't forget — to make them mindful. (Latin monēre is in fact a cousin of the English word mind.) From this single idea of "making someone aware," the root fans out in several directions.

The most literal sense is watching and warning. A monitor was originally "one who warns" — a reminder, an adviser, a prefect who kept an eye on a class. Today a monitor watches a patient's heartbeat or displays your computer's output, and to monitor something is to keep watching it for any sign of trouble. Monitoring is that watchful activity made into a noun.

A second branch turns the warning toward someone. ad- (to, toward) + monēre gives admonish: to warn someone firmly, to scold gently. The noun admonition (and the rarer admonishment) is that warning; admonitory describes the tone of one.

A third branch moves the warning forward in time. pre- (before) + monēre gives premonition: a warning that arrives before the event — that uneasy feeling that something bad is coming. Premonitory signs are the symptoms that warn you in advance.

A fourth branch is the loveliest leap: a monument. Built from monēre + -ment, it is literally "a thing that reminds" — a statue, a tomb, an arch raised so that future generations will remember. From the idea of something grand and lasting comes monumental: huge, imposing, of historic weight.

Finally, monēre can mean "call to mind, call together." sub- (here, secretly/up) + monēre gives summon: to call someone formally to appear, or to call up your own courage from within.

The money branch is the famous surprise. Romans minted their coins at the temple of the goddess Juno Monēta — Monēta being a title meaning "the Warner" (legend says her sacred geese once warned Rome of an attack). The mint took its name from her: monēta came to mean "the place where coins are struck," then "coin," then "money" itself. This is why money, monetary, monetize and moneyed share the same root as monument and monitor — the thread is the warning goddess, not the cash.

The pattern: mon is always about putting something in the mind. A prefix tells you when or which way the warning points — pre- (before), ad- (at someone), sub- (call up) — while the coin branch is a historical accident of where Rome happened to build its mint.