==Etymology==
This etymological discussion is simply wrong in so many ways:
The Greek name tigris comes from the Old Persian word for "tiger" and means "the fast one". It might also be argued to come from Kurdish too. In Kurdish "Tir" means arrow. This means that the river is quick and fast like an arrow.Tîj-Tûj means sharp, pointing and cutting. Since the letter "j" doesn't exist in Greek Tîj-Tûj became Tig later Tigr.In Greek at the end of words -is sonex is used (Tîj-Tijr-Tig-Tigr-Tigris). 

First of all, the Persian for "tiger" is babr, not tigr or anything like it.  The Greek word "tigris" meaning "tiger" may be related to Persian words within the same family as "*tigr", but that is not the Persian meaning of the words.

Second, the Kurdish (and Farsi) word for "arrow", tir, comes from Middle Persian tigr  which also means "arrow".

Third, the word tij (or rather tiz) "sharp" is certainly related to tigr, but they belong to the same word family  they are not the same word.

I'll try to come up with something better.