Oscan úp "at," Venetic op "from"
Ancient Greek ἔπι (épi) "on," Mycenaean e-pi- 'id.'
Armenian ew "also"
Sanskrit ápi "by," Avestan aipi 'id.'
On the word *h1opi̯, Sihler (1995) writes, "Some see in these forms various cases of an otherwise lost root-noun meaning literally 'back.' The 'on' sense may have something to do with pack animals or riding."