The Thracian word opa
Word opa
Meaning water
See also Proto-Indo-European: *ab- ‘water, river’
Avestan: āp- ‘water’
Synonyms achel-, iuras, mar

Comments
E.g Scenopa

Other words that might be of interest
ala ‘current, stream’, alta ‘current, stream’, arma ‘swamp’, ars ‘to flow’, arta(s) ‘river’, e(i)b ‘to flow’, kaba(s) ‘bog, swamp’, kalsas ‘dry, dried up’, ostas ‘river mouth’, pala ‘swamp’, sara ‘river’, sind(u)- ‘river’, strumon ‘river’, krisos ‘river name’