From Proto-Italic *aos, early *ajos, from Proto-Indo-European *h₂éyos.
However, cf. Ringe (2017: 311, fn.32) who notes that “an alternative possibility is that [Proto-Germanic *aiz] actually reflects a preform *áys or *h₂áys, as Lat aes must (Michael Weiss, p.c.).”
Cognate with English ore.