Thesaurus

Synonyms for Frightful include:

abominable, alarming, appalling, atrocious, awful, bad, baleful, bloodcurdling, bonzer, chilling, corked, corky, crappy, creepy, creepy-crawly, deplorable, dire, direful, dismaying, disobedient, distressing, dread, dreaded, dreadful, evil, exceeding, exceptional, extraordinary, extraorinaire, fantastic, fearful, fearsome, forbidding, formidable, frightening, frightful, ghastly, grand, great, grim, grisly, gruesome, hair-raising, hairy, hard, hopeless, horrendous, horrible, horrid, horrific, horrifying, howling, icky, ill, incomparable, incompetent, lamentable, lousy, macabre, marvellous, marvelous, mediocre, menacing, minacious, minatory, mischievous, naughty, negative, nightmarish, no-good, olympian, ominous, one, painful, petrifying, phenomenal, pitiful, poor, preternatural, pretty, prodigious, pyrotechnic, rare, rattling, redoubtable, remarkable, rotten, rubber, sad, scarey, scary, severe, shivery, shuddery, sick, singular, sinister, some, sorry, special, stinking, stinky, stupefying, surpassing, swingeing, terrible, terrific, terrifying, threatening, tough, tremendous, ugly, uncanny, uncommon, uncomparable, uncool, unfavorable, unfavourable, unnerving, unskilled, unspeakable, unsuitable, unusual, wonderful, wonderworking, wondrous, worse, worst

frightful is a ADJ.