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.

What does Postmeridian mean?

: occurring after noon : of or relating to the afternoon the postmeridian hours of the day.

What is meaning of anti Meridian?

: occurring before noon : of or relating to the forenoon antemeridian chores at 9 o'clock — compare ante meridiem.