A particular instance, version, or school thereof; a particular theory of knowledge.
The branch of philosophy dealing with the study of knowledge; theory of knowledge, asking such questions as "What is knowledge?", "How is knowledge acquired?", "What do people know?", "How do we know what we know?", "How do we know it is true?", and so on.
Something theorised; a theory.
The development of something beyond its obvious and practical scope.
The act of constructing a theory.