song of Simeon

from The Collaborative International Dictionary of English v.0.48

Nunc dimittis \Nunc" di*mit"tis\ [L. nunc now + dimittis thou
   lettest depart.] (Eccl.)
   The {song of Simeon} (--Luke ii. 29-32), used in the ritual
   of many churches. It begins with these words in the Vulgate.
   [Webster 1913 Suppl.]