From G2204 (zeΕ, to boil). Literally 'boiling hot.' Used exclusively in Revelation 3:15-16 for the Laodicean church.
Zestos is what Jesus wants: 'I would thou wert cold or hot.' Lukewarm is nauseating. Hot water healed (Hierapolis springs); cold water refreshed. Lukewarm was useless. The word demands a decision: passionate commitment or honest rejection. Comfortable indifference β the temperature at which nothing happens β is the worst spiritual condition.