adj. 25B6; adjective
the hellish face of Death : INFERNAL, Hadean; diabolical, fiendish, satanic, demonic; evil, wicked.
(informal) a hellish week : HORRIBLE, rotten, awful, terrible, dreadful, ghastly, horrid, vile, foul, appalling, atrocious, horrendous, frightful; difficult, unpleasant, nasty, disagreeable; stressful, taxing, tough, hard, frustrating, fraught, traumatic, gruelling; informal murderous, lousy; Brit. informal beastly; N. Amer. informal hellacious.
angelic, wonderful.
25B6; adverb (Brit. informal) it's hellish hard work : EXTREMELY, very, exceedingly, exceptionally, tremendously, immensely, intensely, unusually, decidedly, particularly, really, truly, mightily; most, so; N. English right; informal terrifically, awfully, fearfully, terribly, devilishly, majorly, seriously, ultra, oh-so, damn, damned; Brit. informal ever so, well, bloody, dead; N. Amer. informal real, mighty, awful; informal, dated devilish; archaic exceeding.
moderately.