The Collaborative International Dictionary of English v.0.48:

Yule \Yule\ ([=u]l), n. [OE. yol, [yogh]ol, AS. ge['o]l; akin to
   ge['o]la December or January, Icel. j[=o]l Yule, Ylir the
   name of a winter month, Sw. jul Christmas, Dan. juul, Goth.
   jiuleis November or December. Cf. Jolly.]
   Christmas or Christmastide; the feast of the Nativity of our
   Savior.
   [1913 Webster]

         And at each pause they kiss; was never seen such rule
         In any place but here, at bonfire, or at Yule.
                                                  --Drayton.
   [1913 Webster]

   Yule block, or Yule log, a large log of wood formerly put
      on the hearth on Christmas eve, as the foundation of the
      fire. It was brought in with much ceremony.

   Yule clog, the yule log. --Halliwell. W. Irving.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Yule log
    n 1: large log traditionally burned at Christmas