uneasy or fearful about something that might happen

apprehensive for the safety of the mountain climbers.

quick to learn or understand.

perceptive; discerning (usually fol. by of ).

adjective

at ease , calm , quiet , unafraid , undoubting , unfearful , unsuspicious , unworried

adjective

afraid , alarmed , biting nails , butterflies , concerned , disquieted , doubtful , feel in bones , foreboding , frozen * , get vibes , have a hunch , have cold feet , have funny feeling , have stage fright , hung up * , in a cold sweat , in a dither , in a sweat , jellyfish , jittery , jumpy , lily-livered * , mistrustful , running scared , scaredy-cat , shaky * , stiff , suspicious , troubled , uncertain , uneasy , uptight , weak , worried , worried sick , aghast , fearful , fearsome , funky , panicky , anxious , apt , conscious , discerning , misgiving , morbid , nervous