What is a 'greymuzzle'?
A term used years ago in the therian community, first on the old alt.horror.werewolf (AHWW) site, to denote someone who either was physically older (like over 30 in my experience), or who had been a member of the community for several years. Usually, they were both. Me personally, I thought if someone was in the community longer than 10 years, they knew what they were talking about and were thus, a greymuzzle.
However, it's largely fallen into disuse because of people calling themselves greymuzzles and talking about therianthropy, but actually being wrong in their facts. It was also used by people on personal power trips who associated the term for personal gain but who then didn't actually know what they were talking about. It tended to create elitism. So basically a few idiots appropriated the term and ruined it for actual greymuzzles.
In a few cases, greymuzzle was also used to identify a famous therian; that is, someone easily recognized as being therian within any therian community.
Basically someone who's been in the therian community for many years, is over a certain age, and knows what they're talking about with regards to therian-related topics.
All of that being said, such a term has not been used frequently in years and I doubt it's actually needed.