River of Florence and Pisa (4)
I believe the answer is:
arno
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">river of florence and pisa</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 arno that I've seen before include "River in central Italy" , "Italian river" , "25's river" , "River flowing through Florence and Pisa" , "River of 4 down?" .)