Totally unusable, for a fn. You may get away with it in the mn position though. But I fear even then many would think the Tigris was a female tiger. :-/
By the way, you've reminded me of the feminine name Ivria. I once saw it in a name book meaning, "from the Euphrates
River region." Since I wasn't able to find it anywhere else I put it down to another crackpot entry in a dubious name book. But oh, how I wanted it to be real. If anyone reading this can say for sure I'd love to know.