I have a computer science background. In our world, there usually is an organization publishing standard documents for certain areas (e.g. W3C has Web standards, IETF publishes Internet-related network standards as RFCs, for programming languages, frameworks, libraries the company/developers publish a documentation like Oracle's official Java documentation, Microsoft's MSDN for .NET and so forth).
For most mathematical concepts, one can find a definition in an introductory-level book on that subject. However, how can one know that this definition is universally accepted by most mathematicians around the world? Is there any central source for definitions regarding basic concepts of logic, set theory, abstract algebra etc.?
Or, put another way: How can one know that a description in a book for beginners was not intentionally simplified to facilitate understanding?
I would suppose one has to look up the original publication where a concept was first described (possibly in a way that would be considered "outdated" by now), or am I missing something here?
Perhaps the best way to find the "standard" definition of something is to look up a "standard" textbook on the subject (for instance, Walter Rudin's books on Analysis, or Munkres book on Topology). These textbooks have distilled many years of research into fairly accessible material, and looking up the original papers would be akin to re-inventing the wheel.
I am afraid there may not be a better solution to your problem - many fundamental concepts have many equivalent definitions that are best understood in the context within which they arose, so it might be hard to pin down one "dictionary".