In ancient greek(attic), the root of πρέσβυς is πρεσβ-, but why do we use presby- as a prefix?
These might help.
The Latin letter y is often used to translate the Greek υ.
“Presbyterian” as I understand means “government by elders”. The lay members of ruling board of a Presbyterian (USA) congregation are called “ruling elders”, as distinct from the clergy, who are styled “teaching elders”.
And, LIddell & Scott’s Intermediate lists the word πρεσβυτέριον, “a council of elders”, and sources it to the New Testament.
Contents deleted, having been posted in error.