Edgar Polome suggests that Greek (Arcadian) Pan and Vedic Pusa
are reflexes of the same IE god, or at least, as a late development in
the Indo-Iranian and Greek axis in post PIE times. Both Pan and Pusa are
pastoral gods, protectors of the flock.
The form EIEC gives is *péh2uson, (macron over o). It is also connected
to Gaulish or Venetic Puso, and Messapic Pauso (all are proper names). Polome
says this would be built on *peh2 'protect,
feed (cattle)'.
Pan is just the sort of divinity you'd expect pastoralists
would have, one not too complicated in his functions, nor too involved in
cosmology.
Pusan is said to have many of Pan's characteristics, but here,
he's better connected, with Surya the sun-daughter as his wife; he's supposed to
be the best of all charioteers. He also has underworld functions.
Mark.