The Collaborative International Dictionary of English v.0.48:

Caber \Ca"ber\ (k[=a]"b[~e]r), n. [Gael. cabar.]
   A pole or beam, esp. one used in Gaelic games for tossing as
   a trial of strength.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

caber
    n 1: a heavy wooden pole (such as the trunk of a young fir) that
         is tossed as a test of strength (in the Highlands of
         northern Scotland)