dreadful Play adjectiveCausing or involving great suffering, fear, or unhappiness; extremely bad or serious. SYNONYMS alarmingappallingawfulcalamitousdiredistressingfearfulfrighteningfrightfulghastlygrievousgrimgrislygruesomeharrowinghideoushorrendoushorriblehorrifyingmonstrousshockingterribleterrificterrifyingtragicunspeakable