Animal developing a growth (7)
I believe the answer is:
warthog
'animal' is the definition.
(thesaurus)
'developing a growth' is the wordplay.
'developing' indicates anagramming the letters (letters developed into a new form).
'a'+'growth'='agrowth'
'agrowth' anagrammed gives 'WARTHOG'.
(Other definitions for warthog that I've seen before include "Beast" , "African native" , "African wild pig" , "Wild boar of Africa" , "A growth (anag) - African animal" .)