adj. 25B6; adjective
they are fearful of being overheard : AFRAID, frightened, scared (stiff), scared to death, terrified, petrified; alarmed, panicky, nervy, nervous, tense, apprehensive, uneasy, worried (sick), anxious; informal jittery, jumpy; Brit. informal in a (blue) funk; archaic afeared, affrighted.
the guards were fearful : NERVOUS, trembling, quaking, cowed, daunted; timid, timorous, faint-hearted, nervy; informal jittery, jumpy, twitchy, keyed up, in a cold sweat, a bundle of nerves, like a cat on a hot tin roof; Brit. informal having kittens, like a cat on hot bricks; N. Amer. informal spooky.
a fearful accident : TERRIBLE, dreadful, awful, appalling, frightful, ghastly, horrific, horrible, horrifying, horrendous, terribly bad, shocking, atrocious, abominable, hideous, monstrous, gruesome.
(informal) he was in a fearful hurry : (VERY) GREAT, extreme, real, dreadful; informal terrible.