To intonate is to speak in a deliberate, almost musical way. Most poets intonate when they read their poems aloud.
You'll intonate when you're speaking carefully to someone who can't hear well, and also when you're giving a speech. Chanting or reciting a story, song, or piece of verse also requires you to intonate — modulating the way your voice rises and falls as you speak. Intonate comes from the Medieval Latin intonare, "speak according to tone," from the Greek root tonos, "string," or "pitch."