In the highly-controlled society featured in The Giver, the rules govern a strict "precision of language." The irony comes in when the reader realizes that, in a world with no real depth of emotion, many words have become hollow and meaningless. "Love," for example, has no use in this world. Terms like "apology" and "feelings," as well as specific reactions of "anger" or "jealousy" are used daily, though in reality they don't reflect those actions or emotions.
The titles "Giver" and "Receiver" are ironic in meaning in The Giver.