a.m.

adverb1

1. •
   in the hours after midnight and before 12 in the middle of the day

   • Greenfield … Monday thru Friday, 9 to 12 a.m. — 1967

adjective1

1. •
   Initialism of ad modum.

noun2

1. •
   Initialism of Master of Arts.
2. •
   Initialism of anno mundi.