The Collaborative International Dictionary of English v.0.48:

Hail \Hail\, interj. [See Hail, v. t.]
   An exclamation of respectful or reverent salutation, or,
   occasionally, of familiar greeting. "Hail, brave friend."
   --Shak.
   [1913 Webster]

   All hail. See in the Vocabulary.

   Hail Mary, a form of prayer made use of in the Roman
      Catholic Church in invocation of the Virgin. See Ave
      Maria.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Hail Mary
    n 1: a salutation to the Virgin Mary now used in prayers to her
         [syn: Ave Maria, Hail Mary]