Americium

(Latin: before midday) The time interval from midnight to midday; Also called: A.M., a.m., ante meridiem.
1 airmail.
2 Air Medal.
3 [Latin anno mundi] in the year of the world — often printed in small capitals.
4 ante meridiem — often not cap and often punctuated.
5 [New Latin artium magister] master of arts.

ante meridiem
Abbreviation for ante meridiem (Latin “before noon”).

See amplitude modulation.
In physics, abbreviation for amplitude modulation, one way in which radio waves are altered for the transmission of broadcasting signals. AM is constant in frequency, and varies the amplitude of the transmitting wave in accordance with the signal being broadcast.

First person singular form from the verb 'to be.'