thrombocytopenia Syllabification: (throm·bo·cy·to·pe·ni·a)Pronunciation: /ˌTHrämbōˌsītəˈpēnēə/Definition of thrombocytopenia noun Medicine deficiency of platelets in the blood. This causes bleeding into the tissues, bruising, and slow blood clotting after injury. Origin: 1920s: from thrombocyte + Greek penia 'poverty'thrombocytopenia in other Oxford dictionaries Definition of thrombocytopenia in the British & World English dictionary