Three words Jonas learns new meanings for are starving, love, and release.
Jonas has always known only a life of sameness. Until he begins his training as Receiver of Memory, he does not know about colors, love, pain, or emotions.
The first word that Jonas learns a new meaning for is starving. Jonas’s community carefully rations food, so everyone gets exactly as much as they need and no more. Jonas is reprimanded for using the word starving when he is only hungry.
He was not starving, it was pointed out. He was hungry. No one in the community was starving, had ever been starving, would ever be starving. To say "starving" was to speak a lie. (ch 9, p. 70)
Yet, in a memory Jonas experiences starvation.
"Why?" Jonas asked him after he had received a torturous memory in which he had been neglected and unfed; the hunger had caused excruciating spasms in his empty, distended stomach. (ch 14, p. 110-1)
Jonas also learns the meaning of the word love when he experiences a memory of a holiday where a family celebrates with grandparents. When Jonas goes home, he asks his parents if they love him. His father is amused and lectures him for not using precise language.
"Your father means that you used a very generalized word, so meaningless that it's become almost obsolete," his mother explained carefully. (ch 16, p. 127)
Jonas is shocked that his parents consider the word love meaningless, because he has seen that it has meaning. He begins to realize that his parents do not love him, will not love him, and do not even know what love is. It is another point of separation, distancing him from the community.
Jonas is not sure what release means. Most people in his community do not seem to know. They just know the person who is released is never seen again. For some reason, they never seem to question where the person goes.
For a contributing citizen to be released from the community was a final decision, a terrible punishment, an overwhelming statement of failure. (ch 1, p. 2)
It is not until long after Jonas begins his training that The Giver finally tells him what release really is, when Jonas asks to see a Ceremony of Release of an infant twin that his father conducted. Twins are not allowed in the community. They are weighed, and the smaller one is released. By then, Jonas had seen death in the memories.
He killed it! My father killed it! Jonas said to himself, stunned at what he was realizing. He continued to stare at the screen numbly. (ch 19, p. 150)
This is the point when Jonas realizes that he has to leave the community for good. So he does. When he finds out baby Gabe is going to be released for not being able to sleep through the night, Jonas takes him with him.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.