γνῶσις
Gnosis
Spiritual knowledge — knowing through encounter, not reasoning
Gnosis in the Philokalia does not carry the Gnostic connotations the word has acquired in some Western discussions. It refers to the direct, experiential knowledge that comes through the intellect (nous) rather than through the discursive reason (dianoia). It is knowledge that arises from contemplation and spiritual perception — knowing God not through reasoning about God but through direct encounter.
Diadochos of Photiki and Maximos the Confessor both use gnosis to describe the fruit of sustained contemplative practice: a way of knowing that is qualitatively different from intellectual understanding. You can read about fire or you can put your hand near the flame. The first is dianoia. The second is gnosis.