The word lyric came to be used for the "words of a song"; this meaning was recorded in 1829. The common plural predominates contemporary usage. Use of the singular form 'lyric' remains acceptable, yet is considered erroneous in referring to a singular song word as a 'lyric'.
A combination of words when spoken "sung" in a musical fashion would create in the ear of the recipient the combined effect of the sound of a musical instrument in the voice and the delivery of a message in the words which would have a succinct and direct intention to evoke thought or emotion.