Grossly offensive to decency or morality; causing horror:
— A hideous pattern of injustice.

synonyms: horrid, horrific, outrageous.

Roget 846: ugly, ugly as sin, ugly as a toad, ugly as a scarecrow, ugly as a dead monkey; plain, bald (unadorned) 849; homely; ordinary, unornamental^†, inartistic; unsightly, unseemly, uncomely, unlovely; unshapely; sightless, seemless^†; not fit to be seen; unbeauteous^†, unbeautiful; beautiless^†, semibeautiful; shapeless etc. (amorphous) 241.    misshapen, misproportioned^†; monstrous; gaunt etc. (thin) 203; dumpy etc. (short) 201; curtailed of its fair proportions; ill-made, ill-shaped, ill-proportioned; crooked etc. (distorted) 243; hard featured, hard visaged; ill-favored, hard-favored, evil-favored; ill-looking; unprepossessing, unattractive, uninviting, unpleasing.    graceless, inelegant; ungraceful, ungainly, uncouth, stiff; rugged, rough, gross, rude, awkward, clumsy, slouching, rickety; gawky; lumping, lumpish^†; lumbering; hulky^†, hulking; unwieldy.    squalid, haggard; grim, grim faced, grim visaged; grisly, ghastly; ghost like, death like; cadaverous, grewsome^†, gruesome.    frightful, hideous, odious, uncanny, forbidding; repellant, repulsive, repugnant, grotesque, bizarre; grody [Coll.], grody to the max [Coll.]; horrid, horrible; shocking etc. (painful) 830.    foul etc. (dirty) 653; dingy etc. (colorless) 429; gaudy etc. (color) 428; disfigured etc. v.; discolored.    ... show more

Roget 830: causing pain, hurting etc. v.; hurtful etc. (bad) 649; painful; dolorific^†, dolorous; unpleasant; unpleasing, displeasing; disagreeable, unpalatable, bitter, distasteful; uninviting; unwelcome; undesirable, undesired; obnoxious; unacceptable, unpopular, thankless.    unsatisfactory, untoward, unlucky, uncomfortable.    distressing; afflicting, afflictive; joyless, cheerless, comfortless; dismal, disheartening; depressing, depressive; dreary, melancholy, grievous, piteous; woeful, rueful, mournful, deplorable, pitiable, lamentable; sad, affecting, touching, pathetic.    irritating, provoking, stinging, annoying, aggravating, mortifying, galling; unaccommodating, invidious, vexatious; troublesome, tiresome, irksome, wearisome; plaguing, plaguy^†; awkward.    importunate; teasing, pestering, bothering, harassing, worrying, tormenting, carking.    intolerable, insufferable, insupportable; unbearable, unendurable; past bearing; not to be borne, not to be endured; more than flesh and blood can bear; enough to drive one mad, enough to provoke a saint, enough to make a parson swear, enough to gag a maggot.    shocking, terrific, grim, appalling, crushing; dreadful, fearful, frightful; thrilling, tremendous, dire; heart-breaking, heart-rending, heart-wounding, heart-corroding, heart-sickening; harrowing, rending.    odious, hateful, execrable, repulsive, repellent, abhorrent; horrid, horrible, horrific, horrifying; offensive.    nauseous, nauseating; disgusting, sickening, revolting; nasty; loathsome, loathful^†; fulsome; vile etc. (bad) 649; hideous etc. 846.    sharp, acute, sore, severe, grave, hard, harsh, cruel, biting, caustic; cutting, corroding, consuming, racking, excruciating, searching, grinding, grating, agonizing; envenomed; catheretic^†, pyrotic [Med.].    ruinous, disastrous, calamitous, tragical; desolating, withering; burdensome, onerous, oppressive; cumbrous, cumbersome.    ... show more

So extremely ugly as to be terrifying:
— A hideous scar.

synonym: repulsive.

Polish: odrażający, poczwarny