Hoofed mammal (5)
(Other definitions for horse that I've seen before include "This common sense is of equine origin" , "Animal with withers" , "Nag, hack" , "punch, perhaps" , "Ridden animal" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">hoofed mammal</span>' is the definition.<br/ ><span class="explanation-format__explanation">(hippo is a kind of hoofed mammal)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for hippo that I've seen before include "Large semi-aquatic mammal (abbr)" , "Wallowing creature" , "Thick-skinned type" , "Semiaquatic animal" , "one that's large and fleshy" .)