The Collaborative International Dictionary of English v.0.48:

Christmastide \Christ"mas*tide`\, n. [Christmas + tide time.]
   The season of Christmas.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Christmastide
    n 1: period extending from Dec. 24 to Jan. 6 [syn: Christmas,
         Christmastide, Christmastime, Yule, Yuletide,
         Noel]