Exothen (G1855) is an adverb meaning 'from without' or 'on the outside' — the spatial and metaphorical exterior. It appears in Jesus's condemnation of the Pharisees (Matt 23:25-28, Luke 11:39-40), Paul's description of external hardships (2 Cor 7:5), and the description of the New Jerusalem's exterior (Rev 21:18). The word defines the surface versus the interior — the appearance versus the reality.
Jesus used exothen most powerfully in the woes against the Pharisees: they cleansed the outside (exothen) of the cup while the inside was full of extortion (Matt 23:25). The whitewashed tombs were beautiful exothen but full of dead men's bones within (Matt 23:27). This inside/outside distinction cuts to the heart of authentic versus performative religion. God looks at the heart (1 Sam 16:7); humans see only the exothen. The Gospel works from the inside out — a transformed heart produces transformed exterior behavior, not the reverse.