Entry 1 sense Webster, 1913 Lethargic /(lē̇*thär"jĭk)/ · Le·thar·gic · IPA /ləˈθɑɹd͡ʒɪk/ 01 a. Pertaining to, affected with, or resembling, lethargy; morbidly drowsy; dull; heavy. 1. Pertaining to, affected with, or resembling, lethargy; morbidly drowsy; dull; heavy.