A lyricist is someone who writes the words for modern songs or for musicals.
N-COUNT
lyricist
¦ noun a person who writes the words to popular songs.
lyrist
¦ noun
1. 'l???r?st a person who plays the lyre.
2. 'l?r?st a lyric poet.
Wikipedia
Lyricist
A lyricist is a person who writes lyrics (the spoken words), as opposed to a composer, who writes the song's music which may include but not limited to the melody, harmony, arrangement and accompaniment.