Origin (etymology) of the name Mithridates

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Mithridates or Mithradates (in Greek, Mιθριδάτης or Mιθράδάτης) is the Hellenistic form of an Iranian theophoric name meaning "given by Mithra", being thus a Greek historiographic adaption of Old Iranian *Mithradata-:

1) First element from Indo-European mitros, Proto-Indo-Iranian *mitras, an Indo-Iranian divinity. Pokorny refined Meillet's mei- as "to bind." Combining PIE zero-grade mi- with the "tool suffix" -tro- "that which [causes] ..." (also found in man-tra-, "that which causes to think"), then literally means "that which binds" and thus "covenant, treaty, agreement, promise, oath" etc; cf. Gk. Hom. μίτρη “Gurt; head fascia, Withra”; doubtful μίτος “Einschlagfaden”; Ltv. mìemuri, meimuri “Femerstricke”. Pokorny's interpretation links it with PIE root mei-, "to fasten, strengthen", which may be found in Latin moenia "city wall, fortification", and in an antonymic form, Old English (ge)maere "border, boundary-post".

2) Second element from participle of dō-, "give"; compare participle Lat. datus “bestowed” = falisk. datu “given, delivered, given up, surrendered “,vest. data “ been delivered, given up, surrendered “, päl. datas “ been delivered, given up, surrendered" (: Gk. δοτός); compare also Ind. participle ditá-ḥ (uncovered), secondary dattá-ḥ, zero grade in ā̈-t-tá-ḥ, prá-t-ta-ḥ “devoted”; BUT, ablaut. in tvā-dāta-ḥ “ you gave from", Av. dāta-. Therefore translated as the general IE zero-grade datós.

Hence MIE Mitrodátos, "given by Mitra (promise, oath)".