With its connotation of gossiper, this archaic word for grandmother has earned the “low” tag.  It is the feminine counterpart to “gaffer”, but The Hobbit does not use that word.  Instead, in this instance “gammer” is paired with “greybeards”

• 10.018 and laughed at the greybeards and gammers who said

“gammer, n.” OED Online. Oxford University Press, March 2015. Web. 20 May 2015.