WordNet sense 1 (extremely distressing):

frightful

WordNet sense 2 (having undesirable or negative qualities):

bad

WordNet sense 3 (lacking in courage and manly strength and resolution; contemptibly fearful):

pusillanimous

WordNet sense 4 (lacking conviction or boldness or courage):

timid

WordNet sense 5 (easily frightened):

chicken, yellow

WordNet sense 6 (lacking courage; ignobly timid and faint-hearted):

cowardly

WordNet sense 7 (timid by nature or revealing timidity):

timorous, trepid

WordNet sense 8 (causing fear or dread or terror):

awful, dire, direful, dread, dreaded, dreadful, fearsome, frightening, horrendous, horrific, terrible

WordNet sense 9 (causing alarm or fear):

alarming

WordNet sense 10 (filled with fear or apprehension):

afraid