The Collaborative International Dictionary of English v.0.48:

Hallowmas \Hal"low*mas\ (h[a^]l"l[-o]*m[.a]s), n. [See Mass
   the eucharist.]
   The feast of All Saints, or Allhallows.
   [1913 Webster]

         To speak puling, like a beggar at Hallowmas. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Hallowmas
    n 1: a Christian feast day honoring all the saints; first
         observed in 835 [syn: All Saints' Day, Allhallows,
         November 1, Hallowmas, Hallowmass]