1. Overgrown with moss
   "The moss-grown stones of the old wall";
   - mossy
    
2. [N. Amer, informal] (used pejoratively) out of fashion; old fashioned
   "moss-grown ideas about family life";
   - fogyish [informal], mossy [N. Amer, informal], stick-in-the-mud [informal], stodgy, fogeyish

See also: covered, daggy [Austral, NZ, informal], unfashionable, unstylish