Genethliac \Ge*neth"li*ac\, n. 1. A birthday poem. 2. One skilled in genethliacs. Genethliac \Ge*neth"li*ac\, a. [L. genethliacus, Gr. ?, fr. ? belonging to one's birth, gene`qlh birth, fr. gi`gnesqai to be born.] Pertaining to nativities; calculated by astrologers; showing position of stars at one's birth. --Howell.