The Collaborative International Dictionary of English v.0.48:

Am \Am\ [AS. am, eom, akin to Gothic im, Icel. em, Olr. am,
   Lith. esmi, L. sum., Gr. ?, Zend ahmi, Skr. asmi, fr. a root
   as to be. ?. See Are, and cf. Be, Was.]
   The first person singular of the verb be, in the indicative
   mode, present tense. See Be.
   [1913 Webster]

         God said unto Moses, I am that am.       --Exod. iii.
                                                  14.
   [1913 Webster]

WordNet (r) 3.0 (2006):

A.M.
    adv 1: before noon; "let's meet at 11 A.M." [syn: ante
           meridiem, A.M.]
    adj 1: before noon [syn: ante meridiem, a.m.]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "AM":
   Ack Emma, FM, PM, amplitude modulation, ante meridiem,
   double sideband, foreday, forenoon, grey-eyed morn,
   incense-breathing morn, matins, modulation, morn, morning,
   morning time, morntime, side frequency, sideband, this AM,
   this morning, waking time



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

AM
       Amplitude Modulation


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

AM
       Active Matrix (LCD)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

AM
       Asynchronous Mode