A lyric was originally the words of a lyric poem suitable for setting to the music of a lyre, as per the roving troubadours of old. This is from Webster's Collegiate:

1 lyric \'lir-ik\ adj 1: suitable for singing to the lyre or for being set to music and sung 2 a: expressing direct usu. intense personal emotion<~poetry> b: EXUBERANT, RHAPSODIC 3 of an opera singer: having a light voice and a melodic style -- compare DRAMATIC

2 lyric n 1: a lyric composition; specif: a lyric poem 2 pl the words of a popular song or musical-comedy number

Note 2:2 stresses plural for the words of a song

lyricist n: a writer of lyrics

lyrist n : 1. \'ly(e)r-est\ a player on the lyre 2. \'lir-est\ : LYRICIST

(Oh, and lyre is from the ME lire, OF lyra, and is derived from Greek...so there's something for you, Dr. Bill)