From mihi (“to me”, dative singular of ego (“I”)) + -met (“-self”, intensive suffix).
mihimet
- dative of egomet; to me myself, to my very self
c. 190 BCE – 185 BCE,
Plautus,
Amphitryon 2.1.597:
- Neque, ita mē dī ament, crēdēbam prīmō mihimet Sōsiae, […]
- And gods help me, at first I didn’t even believe my very self, Sosia, […]