Is that really what authority means? I always thought it was along the lines of 'famous guy X says Y so Y must be true'. While a dictionary on the other hand is something which I'd really consider authorative i.e. correct when it's about the meaning of words. So a dictionary's reason of existence, it's whole prupose is explaining the meaning of a word, you could say it states the actual facts. Wehereas some famous guy saying something doesn't make it a fact automatically just because he's famous.