Appt. Is the abbreviation for "appointment". One of the many shortened words used in text speech. APPT. Also found in: Dictionary. Related to APPT: AAPT. Acronym, Definition. APPT, Appointment. APPT, Activated Partial Thromboplastin Time (clotting. Looking for the definition of APPT? Find out what is the full meaning of APPT on stargamesrealonlinecasino.review! 'Appointment' is one option -- get in to view more @ The.