1) Half a day 2) Occurring before noon 
antemeridian, antemeridiem (A.M.) 1. Of or belonging to the forenoon or 'morning'. 2. Before midday; applicable to the hours between midnight and the following noon.antemeridiem Everything has been thought of before, but the problem is to think of it again. —Johann W. von Goethe Related before-word units: antero-; anti-; pre-; pro-.