As a singer/songwriter and musical-theatre performer I've always used and heard lyrics except when referring to a specific word, phrase, or line, in which case we might say, "I'm forgetting the lyric," "What's that lyric?", "Let's change that lyric," something akin to the way an actor might say "my lines" when referring to a large portion of a script, but "I dropped a line" or "I love that line" when referring to one spot or, well, one line. Of course, on the published sheet music it usually reads Music by: and Words by: (a distended period here?...I've never had to place a period after a colon before, how's that work? )