I've never heard of anybody refer to an authoritative server as a "resolver" before. Even the article considers them separate: > any third party who can observ

I've never heard of anybody refer to an authoritative server as a "resolver" before. Even the article considers them separate: > any third party who can observe communication between a client and a recursive resolver, a recursive resolver, or an authoritative server The "recursive" adjective is pretty clearly to distinguish between stub and recursive resolvers.