WordNet sense 1 (extreme in degree or extent or amount or impact):

awful, frightful, tremendous

WordNet sense 2 (beyond what is ordinary or usual; highly unusual or exceptional or remarkable):

extraordinary

WordNet sense 3 (intensely or extremely bad or unpleasant in degree or quality):

severe, wicked, wicked

WordNet sense 4 (in an extreme degree):

intense

WordNet sense 5 (exceptionally bad or displeasing):

abominable, atrocious, dreadful, painful, unspeakable

WordNet sense 6 (causing fear or dread or terror):

dire, direful, dread, dreaded, fearful, fearsome, frightening, horrendous, horrific

WordNet sense 7 (causing alarm or fear):

alarming