"Moss-backed" is an old-fashioned and somewhat obscure word, typically used to describe someone who is stubbornly set in their ways and resistant to change or progress. There are several synonyms that could be used in place of "moss-backed" to convey a similar meaning, including "hidebound," "reactionary," "conservative," "traditionalist," "fossilized," and "ossified." Each of these words suggests rigidity, inflexibility, and a reluctance to deviate from established norms or beliefs. Whether used to describe a person, an institution, or a social or political movement, these synonyms can help to capture the obstinate and unyielding nature of the "moss-backed" mindset.