An ancient Greek stringed instrument [see lyre]. Associated in Archaic vase paintings with Apollo and Artemis (also see Homeric Hymn to Apollo 3. 182-85), "phorminx" as a term used rather interchangeably with "kitharis" (kithara) in Homer's Iliad and Odyssey. There is a certain amount of confusion about the exact relationshipo between the two instruments. For one thing, the verb used in Homer to refer to phorminx playing is kitharizein (κιθαρίζειν). Organologists have called the phorminx a "cradle kithara" to distinguish it from the kithara of the classical period, but Maas and Snyder prefer to keep the two instruments separate. Homer's phorminx was played by professional bards such as Demodokos and Phemias, and Achilles plays to amuse himself in Iliad 9. Gradually the phorminx was replaced as an instrument of choice in favor of other lyre-types, and as its use narrowed, the term began to fade from the Greek vocabulary. In the classical period the phorminx is primarily associated with the cult festivals of Dionysus. The phorminx is similar to the kithara in construction, with a few marked differences: 1) the arms are straighter and more parallel, and were often elaborately carved, 2) the wooden soundbox of the phorminx has a softer, rounder curve to it, and 3), the soundbox almost always displays unique circle or "eye" designs on its face. The painted eyes give the phorminx an animated quality unlike any other lyre, and are always a distinguishing feature. Players generally stood up while they played, though there are some vase paintings in which there player is seated. The instrument is held in front of the body and tipped slightly outward , otherwise it is played and tuned like other members of the lyre family. It has the same number of strings as the kithara (five to seven, with seven being common from the Archaic period onward).
Maas, Martha and Jane Snyder, Stringed Instruments of Ancient Greece, New Haven, Yale University Press, 1989
New Grove Dictionary of Musical Instruments, 3 vols., ed. Stanley Sadic, London, 1984
"Music.9. Instruments," Oxford Classical Dictionary (second ed.), Oxford, 1978