The Collaborative International Dictionary of English v.0.48:

Ambrosian \Am*bro"sian\, a.
   Of or pertaining to St. Ambrose; as, the Ambrosian office, or
   ritual, a formula of worship in the church of Milan,
   instituted by St. Ambrose.
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   Ambrosian chant, the mode of signing or chanting introduced
      by St. Ambrose in the 4th century.
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The Collaborative International Dictionary of English v.0.48:

Chant \Chant\, n. [F. chant, fr. L. cantus singing, song, fr.
   canere to sing. See Chant, v. t.]
   1. Song; melody.
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   2. (Mus.) A short and simple melody, divided into two parts
      by double bars, to which unmetrical psalms, etc., are sung
      or recited. It is the most ancient form of choral music.
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   3. A psalm, etc., arranged for chanting.
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   4. Twang; manner of speaking; a canting tone. [R.]
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            His strange face, his strange chant.  --Macaulay.
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   Ambrosian chant, See under Ambrosian.

   Chant royal [F.], in old French poetry, a poem containing
      five strophes of eleven lines each, and a concluding
      stanza. -- each of these six parts ending with a common
      refrain.

   Gregorian chant. See under Gregorian.
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