WordWeb Online

1. Highly offensive; arousing aversion or disgust
   "a loathful smell";
   - disgusting, disgustful [archaic], distasteful, foul, loathly, loathsome, repellent, repellant, repelling, revolting, skanky [informal], wicked, yucky [informal], gross-out [informal], yukky [informal]
    
2. Causing or able to cause nausea
   "a loathful smell";
   - nauseating, nauseous, noisome, queasy, loathsome, offensive, sickening, vile, vomitous [US]

See also: gut-wrenching, offensive, unwholesome