*mōtan

Wiktionary has it from Proto-Indo-European *meh₂d- (“to encounter, to come”); Köbler gives a doubtful PIE *mōd- "to meet, to come".

Kroonen takes it as a preterite-present probably built on a root from Proto-Indo-European *mod- (“to approach”), the root of Old Armenian մատչիմ (matčʻim, “to approach, come close”).