an·te me·rid·i·em 
(ăn′tē mə-rĭdē-əm)
(ăn′tē mə-rĭdē-əm)adv. & adj. Abbr. AM or am or AM
Before noon. Used chiefly in the abbreviated form to specify the hour: 10:30 AM. See Usage Note at AM.
[Latin ante, before + merīdiem, accusative of merīdiēs, noon.]