The Collaborative International Dictionary of English v.0.48:

Crannog \Cran"nog\ (kr?n"n?g), Crannoge \Cran"noge\ (kr?n"n?j),
   n. [From Celtic; cf. Gael. crann a tree.]
   One of the stockaded islands in Scotland and Ireland which in
   ancient times were numerous in the lakes of both countries.
   They may be regarded as the very latest class of prehistoric
   strongholds, reaching their greatest development in early
   historic times, and surviving through the Middle Ages. See
   also Lake dwellings, under Lake. --Encyc. Brit.
   [1913 Webster]