The Conscience of the King had a kill setting
Or at least a setting that killed the frail old Kodos/Anton Karidian. (Lenore claims she knows how to use the phaser she grabs, but should we really believe her? The phaser would not have been on kill when she grabbed it, and we know stun is lethal at close range against the weak.) Yet a "kill setting" is never really mentioned by name in the episode.
The combining of lethality and the stun setting (perhaps here, but certainly in ST6 and "Samaritan Snare") is rather telling. We're probably not witnessing thirty-three different settings, but rather a combination of something like three main parameters that can be adjusted, each with a dozen notches at most, and probably way fewer.