The Avestan word paoiriia-
Word paoiriia-
Meaning first
See also Proto-Indo-European: *per(hₓ)- ‘first’

Other words that might be of interest
aēuua ‘one’, ašta ‘eight, 8’, xšuuaš ‘six, 6’, θritiia- ‘third’, paṇca ‘five, 5’, bitiia- ‘second’, hapta ‘seven, 7’, caθβarasca ‘four’