Entos (ἐντός) means 'within' or 'inside' — in the interior of something. It appears in two of Jesus's most theologically loaded statements: (1) Luke 17:21, 'the kingdom of God is entos you' (within you / in your midst); and (2) Matthew 23:26, 'first clean the inside [entos] of the cup and dish.' These two uses capture the core of Jesus's teaching on authentic religion: it begins within, not without.
The Luke 17:21 usage has generated centuries of interpretation. Does 'the kingdom of God is entos you' mean it is internal (within each individual) or in your midst (among you as a group)? Many scholars favor 'in your midst' given the audience (Pharisees) and context. Either way, Jesus's point is that the kingdom does not come through external observation or calculation — it is present in an interior or communal reality that requires spiritual perception. The Matthew 23:26 usage is unambiguous: religious reform begins inside, not in external polish. Entos is where transformation must happen.