adjective
horrible, terrifying
Synonyms: appalling, awful, dangerous, daunting, dire, dismaying, dreadful, fearful, fierce, frightful, horrific, imposing, impregnable, intimidating, menacing, redoubtable, shocking, terrible, terrific, threatening
Antonyms: feeble, friendly, harmless, nice, pleasant, powerless, weak
adjective
difficult, overwhelming
Synonyms: all-powerful, arduous, awesome, ballbuster, challenging, colossal, dismaying, effortful, great, hard, impressive, indomitable, intimidating, labored, laborious, mammoth, mighty, murder, onerous, overpowering, powerful, puissant, rough, rough go, staggering, strenuous, tall order, toilsome, tough, tough proposition, tremendous, uphill
Antonyms: easy, not hard, pleasant, trivial