post me·rid·i·em 
(mə-rĭdē-əm)
(mə-rĭdē-əm)adv. & adj. Abbr. PM also PM or pm
After noon. Used chiefly in the abbreviated form to specify the hour: 10:30 PM; a PM appointment. See Usage Note at PM.
[Latin post merīdiem : post, after + merīdiem, accusative of merīdiēs, midday.]