From the Latin words meridies (midday), ante (before) and post (after), the term ante meridiem (a.m.) means before midday and post meridiem (p.m.) means after midday.

Is Meridiem a word?

The term, first recorded in English in 1563, is from Latin: ante (before) and meridiem (midday). ... Under its entry for “a.m.” and “p.m.,” Garner's Modern American Usage (3rd ed.) has this to say: “Some writers, when using the full phrases, mistake meridiem for meridian.”

What is the difference between meridian and Meridiem?

Ante Meridian is a misspelling of: Antimeridian, a meridian at 180° from another or the meridian opposite the prime meridian. Ante meridiem, normally abbreviated a.m., Latin for "before midday"