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.