Lethargic rhymes with:
allergic, analogic, biologic, demagogic, dziedzic, geologic, gynecologic, illogic, immulogic, intelogic, karadzic, logic, magic, majik, neurologic, nonstrategic, nostalgic, pelagic, quadriplegic, silajdzic, strategic, tajik, technologic, tragic, translogic, xylogic, zajic
Lethargic sounds like:
ladders, laterza, lathers, lathouris, latter's, leader's, leaders, leaders', leadwork, leathers, leatrice, lehder's, lethargy, letters, literacy, liters, litters, liturgy, loaders, lodwrick, looters, lotteries, lueders