From: george knysh
> If the hydronym <gerros> is a loose spelling variant****GK: Thank you Piotr. I'll file this away as the
> of *kerros (or *kersos, since <-rr-> and <-rs->
> commonly vary in Greek), it might be a "Thracoid"
> reflex of *krsos 'Black (River)' (for a parallel
> hydronym, cf. Grisia [Jordanes] ~ Krisos = Cris^,
> with syllabic *-r- > Dacian -ri-). A shaky but not
> impossible derivation.