The title suggests that this chapter in Untener will define a homily, yet it never explicitly does. Instead, it extensively describes the preacher's task, from which one may deduce the nature of homilies, though never being directly told what the author thinks they are. What he does think is that all liturgical ministers should "help the flow of what Christ is doing" in the service. The preacher, we are told, has three tasks, namely:
discerning God's action and/or message
"illuminating" the action and/or message for the assembly
doing this on the church's behalf.
The third so-called task is less of a task than a means of performing the preceding two tasks. Central to the preacher's actions, the author tells us, is the fact that God's word is alive and life-giving. The homilist, it seems, works out what that word has to say to his congregation, using not just his own discernment but that of the whole Catholic church. From these impressions, can one work out what a homily is? It is perhaps a means of imparting God's word to a community so that it is not only understood but also bears fruit? This, however, is only conjecture because Untener never says in this chapter what a homily is.
(As a digression, I observe that at least some writing about preaching tends to be about how it is done rather than why it is done. Furthermore, assertions about what techniques are better than others tend to be unsubstantiated.)
If we assume that the bearing of fruit by the congregation is the point of homiletics, we get a bit closer to my desired goal - a mechanism for discovering whether homilies are fulfilling their purpose.