Originally, he didn't need a navel (4)
I believe the answer is:
adam
'originally he didn't' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a navel' is the wordplay.
'navel' becomes 'dam' (I can't justify this - if you can you should believe this answer much more).
'a'+'dam'='ADAM'
'need' acts as a link.
Can you help me to learn more?
(Other definitions for adam that I've seen before include "Father of Cain and Abel" , "Biblical first man" , "- - Bede, novel" , "Eden man" , "Male" .)