The Collaborative International Dictionary of English v.0.48:

Angelus \An"ge*lus\, n. [L.] (R. C. Ch.)
      (a) A form of devotion in which three Ave Marias are
          repeated. It is said at morning, noon, and evening, at
          the sound of a bell.
      (b) The Angelus bell. --Shipley.
          [1913 Webster]

WordNet (r) 3.0 (2006):

angelus
    n 1: the sound of a bell rung in Roman Catholic churches to
         announce the time when the Angelus should be recited [syn:
         angelus bell, angelus]
    2: a prayer said 3 times a day by Roman Catholics in memory of
       the Annunciation