The only references I have ever been able to find about a possible meaning is on the origin of the Scandinavian name Gro or Groa which is said to have a possible link to 'the Celtic word Gruach meaning woman' in several sources
e.g. The Oxford Names Companion (Hanks, Hodges et al, 2002) ;
http://www.halfdan.is/vestur/nofn.htm#GlossG ;
http://www.gaminggeeks.org/Resources/KateMonk/Europe-Scandinavia/Old-Norse/Female.htm