i. e. unshorn, a surname of Apollo and Bacchus, alluding to the eternal youth of these gods, as the Greek youths allowed their hair to grow until they attained the age of manhood, though in the case of Apollo it may also allude to his being the god of the sun, whence the long floating hair would indicate the rays of the sun. (Hom. Il. 20.39, Hymn. in Apoll. 134; Horat. Epod. 15.9; Tib. 1.4. 34; Ov. Met. 3.421, Amor. 1.14. 31; Martial, 4.45.)
[L.S]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890