The word, "gnosis", can have a variety of contexts and meanings, though it tends to be used in a more profound and deeper context. "Gnosis", is more akin to a word, such as awareness-(i.e. The Delphic inscription, Socrates).
The word, "Episteme", is actually, the Greek word for Science. The Modern Greek word for University is, "PanEpisteme", which translates as "All of the Sciences-(Though interestingly, Scientific Schools in Greece are called, Polytechnion). Episteme, is the basis for the word, "Epistemological", which means, "The Theory of Knowledge", though it really means, the theory of scientific, intellectual or philosophical knowledge and inquiry.
If, for example, we take the word, "Fact"...an Epistemologist or an Epistemologically minded person might ask, What is a Fact? or more importantly, How does a fact actually become a fact? How sure are we as to what is factual and what is nonfactual? What is affirmable and what is Apocryphal.
A Gnostic, however-(not to be confused with The Gnostics of the Early Middle Ages), is also interested in a fact, but for different reasons. A Gnostic is interested in a fact as a way of leading to greater self-awareness and self-acknowledgement, thereby reaching a higher or perhaps even a transcendental state of mind and being.
These two words-(like other Ancient Greek words), have a long and continuous history into the Modern Greek language.