Q: My child got back a spelling test in which she was marked wrong for writing “ante meridiem” as the full name of the abbreviation “AM.” The teacher’s spelling list had it as “antemeridian.” Is this some variant I’m unaware of?
A: Your child’s paper should not have been marked wrong.
In fact, “ante meridiem” and “antemeridian” are two different terms. Neither of them is seen much, though, since the first is rarely written out and the second is rarely used at all.
The two-word “ante meridiem” is the term that’s abbreviated as “AM” or “a.m.” Like its counterpart, “post meridiem,” it’s seldom written out.
The Oxford English Dictionary classifies “ante meridiem” as an adverb meaning “before midday; applied to the hours between midnight and the following noon.”
Standard dictionaries agree that the full phrase is uncommon. The American Heritage Dictionary of the English Language (5th ed.), for example, says “ante meridiem” is “used chiefly in the abbreviated form to specify the hour: 10:30 AM.”
The term, first recorded in English in 1563, is from Latin: ante (before) and meridiem (midday).
The other word, “antemeridian,” is labeled in the OED as a “rare” adjective meaning “of or belonging to the forenoon or ‘morning.’ ”
The word, Oxford says, was derived from the Latin adjective antemeridianus (“of the forenoon”), which in turn comes from ante meridiem.
Some standard dictionaries (Longman and Macmillan, for example) don’t have entries for “antemeridian.”
One that does, Merriam-Webster’s Unabridged, gives this example of its usage: “antemeridian chores.” Another, Webster’s New World, has “an antemeridian repast.”
The OED has only one example for the use of “antemeridian” in a sentence, from an 1865 article in the Daily Telegraph of London: “Every[one] had come out in attire that was decidedly ante-meridian.”
The spelling that’s clearly a mistake today is “ante meridian.” It’s either “ante meridiem” or (less likely) “antemeridian.”
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.”
If you can’t remember which is which, go to the dictionary. You’ll usually find at least one of them.