River joining the Tigris (9)
I believe the answer is:
euphrates
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">river joining the tigris</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for euphrates that I've seen before include "running water in Iraq" , "River flowing through Turkey, Syria and Iraq" , "Asian flower" , "some running water in Middle East" , "River joining the Tigris" .)