Source : Webster's Revised Unabridged Dictionary (1913)

Michaelmas \Mich"ael*mas\, n. [Michael + mass religious service;
   OE. Mighelmesse.]
   The feat of the archangel Michael, a church festival,
   celebrated on the 29th of September. Hence, colloquially,
   autumn.

   {Michaelmas daisy}. (Bot.) See under {Daisy}.

Source : WordNet®

Michaelmas
     n : honoring the archangel Michael; a quarter day in England,
         Wales, and Ireland [syn: {Michaelmas Day}, {September 29}]