Entry 1 sense Webster, 1913 Ptosis /(tō"sĭs)/ · Pto·sis · IPA /ˈtoʊ.sɪs/ 01 n. Drooping of the upper eyelid, produced by paralysis of its levator muscle. 1. Drooping of the upper eyelid, produced by paralysis of its levator muscle.(Med.)