WordNet sense 1 (disagreeable to the senses, to the mind, or feelings ):

unpleasant

WordNet sense 2 (exceptionally bad or displeasing):

abominable, atrocious, awful, painful, terrible, unspeakable

WordNet sense 3 (having undesirable or negative qualities):

bad

WordNet sense 4 (causing fear or dread or terror):

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

WordNet sense 5 (causing alarm or fear):

alarming