librettist

n. person who writes the words for an opera

A libretto is the text used in an extended musical work such as an opera, operetta, masque, sacred or secular oratorio and cantata, musical, and ballet. The term "libretto" is also sometimes used to refer to the text of major liturgical works, such as mass and requiem.Libretto (pl. libretti) is an Italian word which translates literally as "little book." It is distinct from a synopsis or scenario of the plot. The relationship of the librettist (that is, the writer of a libretto) to the composer in the creation of a musical work has varied over the centuries, as have the sources and the writing techniques employed.
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Noun
1. author of words to be set to music in an opera or operetta
(hypernym) writer, author
(hyponym) Gilbert, William Gilbert, William S. Gilbert, William Schwenk Gilbert, Sir William Gilbert

n. librettist, person who writes the words for an opera

(n.)
One who makes a libretto.