lyricist
A person who writes the words for songs.
A lyricist is someone who writes the words to songs. While a composer creates the melody (the tune you hum), the lyricist crafts the lyrics (the words you sing). Think of how “The Star-Spangled Banner” needed Francis Scott Key to write the words, even though the melody came from an older British song.
Some musicians write both music and lyrics, but many famous songs come from partnerships: one person composes the tune while the lyricist finds the perfect words to match it. Oscar Hammerstein II was the lyricist for The Sound of Music, writing lines like “raindrops on roses and whiskers on kittens” while Richard Rodgers composed the melody. Lin-Manuel Miranda wrote both music and lyrics for Hamilton, but that's unusual.
A skilled lyricist thinks about how words sound when sung as well as what they mean. They consider rhythm (how syllables fit the beat), rhyme schemes, and which words feel good in your mouth when you sing them. They might spend hours finding exactly the right word, because a lyricist writes for singers and listeners, creating words meant to be performed aloud rather than read silently on a page.
The job requires understanding both language and music: a word might look perfect on paper but sound clumsy when sung, or it might have too many consonants that make it hard to belt out at high volume.