The Collaborative International Dictionary of English v.0.48:

Groyne \Groyne\, n. [Obs.]
   See Groin.
   [1913 Webster]

WordNet (r) 3.0 (2006):

groyne
    n 1: a protective structure of stone or concrete; extends from
         shore into the water to prevent a beach from washing away
         [syn: breakwater, groin, groyne, mole, bulwark,
         seawall, jetty]