Expensive animal, by the sound of it (4)
I believe the answer is:
dear
'expensive' is the definition.
(similar in meaning)
'animal by the sound of it' is the wordplay.
'animal' becomes 'deer' (deer is a type of animal).
'by the sound of it' shows a homophone (sound like).
'deer' sounds like 'DEAR'.
(Other definitions for dear that I've seen before include "Precious" , "Expensive; sweet" , "Costly (but loved!)" , "Darling" , "pet > ducks" .)