Possibly a neologism from miscēre (“to mix”). Cf. the classically indeclinable nūgās, nūgāx (“incompetent, bungling”) and another hapax, miscelliō (“an irresolute, fickle person”).
miscī̆x m or f (indeclinable)
- (hapax, neologism, dubious) Someone who does things half-way or improperly.
c. 27 CE – 66 CE
, Satyricon 45.6
- Nōn est miscī̆x. Ferrum optimum datūrus est, sine fugā, carnārium in mediō, ut amphitheāter videat.
- He doesn't mess around. He's going to give us a proper fight, no running, a public slaughterhouse, so the whole amphitheater can see.
The form and prosody, meaning, usage and even grammatical category of this word are all uncertain.