In a previous post (http://definitionsinsemantics.blogspot.com/2011/11/evolution-of-definitions-problem-of.html) the topic of the IAU's 2006 redefinition of the term "planet" was discussed (see http://www.iau.org/public_press/news/detail/iau0603/).
There are many topics relevant to definitions surrounding this event - one of them is the problem of authority. The International Astronomical Union (IAU) is the organization that came up with the new definition of "planet". Does this make it an authority? It does if we define "authority" as "a source of a definition that publishes, and administers, and supports this definition".
However, the term "authority" carries emotional content also. "Authority" can imply (a) a role of active enforcement; (b) an obligation of obedience upon the body politic. These implications exist because "authority" is a term that defines many concepts, and some of them have to do with enforcement and legislation. Now, some entities that produce definitions also have enforcement roles and legislative roles, but that is not as any direct consequence of producing definitions.
Additionally, the IAU is presumably a collection of scientists, and scientists have an almost priestly aura in contemporary Western civilization. To challenge any scientist is presumably to challenge science. To challenge a scientific consensus is presumably an even worse sin. Just having scientists as an authority seems to add to the intimidating implications when we use the term "authority" when speaking of definitions.
I think the basic stance on this issue must come from the logicians' warning about appeal to authority - the fallacy of argumentum ad verecundiam. First, let us remember that we are only dealing with definitions here, not argumentation such as deduction or induction. The idea is presented above that an authority is a special type of source of a definition. To be an authority, I suggest, means that you are doing more than just creating a definition. You are publishing it so it is available to some form of wider audience. You are administering it, so e.g. there is an orderly way to change it. And you support it - as an authority you stand ready to be consulted on it.
None of this means the definition is of high quality. An authority can do all of the above and create poor quality definitions. An authority can also cause terminological havoc outside of the narrow field of definitions. That it probably why I cannot stop thinking of Pluto as a planet.
We must be very careful, therefore, to understand what an authority is for a definition, and what to expect of an authority. Above all we should not be intimidated. Remember, just because a source of a definition claims to be an authority, or is styled as such, does not mean they automatically produce high quality definitions.