Christian canticle also known as the "Song of Simeon" from Luke 2:29-32. Begins "Nunc dimittis servum tuum" (something like "Now lettest Thou thy servant depart"). Simeon speaks these words to lil' Jesus when he is satisfied that he has seen the Messiah.

Artsy showoffs use the Latin phrase as a noun meaning "permission to go".

To "sing nunc dimittis" is to express readiness to die; in my estimation, a much more eloquent usage of the phrase.