Branches of the animal kingdom (7)
I believe the answer is:
antlers
'branches of the animal kingdom' is the definition.
Although both the answer and definition are plural nouns, I can't understand how one could define the other.
'branches of the animal kingdom' is the wordplay.
'branches' becomes 'antler' (I've seen this before).
'of the animal kingdom' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'antler'+'s'='ANTLERS'
Can you help me to learn more?
(Other definitions for antlers that I've seen before include "Reindeer outgrowth" , "Head branches of 18" , "Branched horns" , "Stag's crowning glory" , "Deer horns" .)