Latin: a.m. & p.m.
The abbreviation a.m. is short for the Latin ante meridiem "before noon". Similarly p.m. is post meridiem "after noon".
e.g. Edward rarely got up before 2 p.m. as he only went to bed at 6 a.m.
a.m. & p.m., cf., e.g., et al., etc., i.e., N.B., P.S., Q.E.D., q.v., viz.
ad hoc, de facto, modus operandi, non sequitur, pro rata, quid pro quo, sic, vice versa.