Definitions for mossbackˈmɔsˌbæk, ˈmɒs-
Random House Webster's College Dictionary
Informal. a person holding very antiquated notions; reactionary.
an old turtle.
a large and old fish, as a bass.
Origin of mossback:
an extremely old-fashioned conservative
A turtle that, because of its age, has a growth of algae on its back.
A very conservative or reactionary person, especially one with old-fashioned views.
a veteran partisan; one who is so conservative in opinion that he may be likened to a stone or old tree covered with moss