Jonas feels that the word “frightened” means a belief that something bad is going to happen.
Frightened meant that deep, sickening feeling of something terrible about to happen. (p. 1, ch 1)
As the book opens, Jonas is trying to decide how he feels. He is worried about something, but decides that “frightened” is not the right word. To Jonas, “frightened” means something bad will happen. In actuality, he does not know what will happen, good or bad. He is worried about the Ceremony of Twelve. At the ceremony, he will be given his job for life. Since he is only twelve, this is a confusing time for Jonas. He does not know what is going to happen.
Jonas finally decides that what he feels is apprehension, not fear. Apprehension just means worry about the future. It means that rather than knowing something bad will happen, you worry that it might.
Jonas realizes he was actually “frightened” when he saw a plane fly over his community, because it was such an uncommon sight that it couldn’t be good. He felt real fear then, that he was in danger. The Ceremony of Twelve is not a danger, but an unknown.
But there was a little shudder of nervousness when he thought about it, about what might happen. Apprehensive, Jonas decided. That's what I am. (ch 1, p. 4)
Jonas’s desire to label everything precisely comes partly from his community’s teachings and partly from his personality. Jonas wants to understand the world. He worries about his future, because everything has always been given to him. In his orderly community, he always knows what’s next. At this point in his life, at the beginning of the book, Jonas is beginning to lose this belief. It foreshadows his loss of faith in the ways of his community, as he slowly begins to lose trust in them.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.