Definition of Musaf in US English:

Musaf

(also Mussaf, Musaph)

noun

Judaism
  • An additional prayer service recited on the Sabbath and festivals, immediately after the Torah reading which follows the morning prayers. Also: an additional Temple sacrifice formerly required to be made on the Sabbath and festival days (now historical).

Origin

Mid 17th century. From post-biblical Hebrew mūsāp (adjective) additional, (noun) addition, additional prayer from yāsap to add, increase.