What is the Greek definition faith?

There isn't one single, universally agreed-upon Greek definition of "faith" that covers all nuances and uses across different philosophical and religious contexts. The ancient Greeks didn't have a single word that perfectly corresponds to the modern English understanding of faith. However, several Greek words relate to aspects of what we might call "faith," each with its own shades of meaning:

* Πίστις (pistis): This is the closest single Greek word to the English "faith." However, its meaning is broader and often translates more accurately as "trust," "belief," "confidence," or "fidelity." It doesn't necessarily imply blind faith or religious belief, but rather a firm conviction based on evidence or trust in a person or authority. In the Septuagint (the Greek translation of the Hebrew Bible), πίστις is used to translate the Hebrew word *'emunah*, which has a religious connotation closer to the modern understanding of faith.

* ἐλπίς (elpis): This word means "hope" or "expectation." While distinct from faith, it's closely related. Hope often involves a degree of faith or belief that something desired will happen.

* πεποίθησις (pepoithesis): This word signifies "trust," "confidence," or "assurance." It carries a stronger sense of certainty than πίστις.

The meaning of these words depends heavily on context. In philosophical discussions, πίστις might refer to a reasoned belief based on evidence, while in religious contexts (especially in the New Testament), it takes on a more spiritual meaning, often involving trust in God or divine authority. The nuance is subtle but important.

Therefore, a concise Greek "definition" of faith is impossible without specifying the context. The most accurate response is that the concept of "faith" in ancient Greek thought is best represented by a range of words, predominantly πίστις (pistis), but with meanings that are less rigidly defined than the modern English equivalent.