Synonyms for Apprehensive (same or very similar meaning)
WordNet sense 1 (quick to understand):
discerningWordNet sense 2 (having the ability to perceive or understand; keen in discernment):
perceptiveWordNet sense 3 (mentally upset over possible misfortune or danger etc):
worriedWordNet sense 4 (lacking a sense of security or affording no ease or reassurance):
uneasyWordNet sense 5 (filled with fear or apprehension):
afraidFrom the ODE community, based on WordNetadd/edit