Answer:
The use of a "Delian healer" to refer to Apollo is called an epithet.
Step-by-step explanation:
An epithet is defined as an ajective or descriptive phrase expressing a quality characteristic of the person or thing mentioned. Apollo has many epithets that include Phoebus, Pythius, Acesius, Lyceius, Belenus, and of course Delian healer. Delian comes from Apollo's birthplace, which is the island of Delos and healer is based on his healing abilities.