An animal with horns returning on foot (5)
I believe the answer is:
ankle
'foot' is the definition.
(thesaurus)
'an animal with horns returning on' is the wordplay.
'animal with horns' becomes 'elk' (I've seen this in another clue).
'returning' is a reversal indicator.
'on' is a charade indicator (letters next to each other).
'elk' written backwards gives 'kle'.
'an'+'kle'='ANKLE'
(Other definitions for ankle that I've seen before include "Joint between foot and leg" , "Bone over foot" , "Location of the talus" , "Major joint in lower limb" , "Leg-joint" .)