Return of one shut in cooler, an innocent person (4)
I believe the answer is:
naif
'innocent person' is the definition.
(I've seen this in another clue)
'return of one shut in cooler' is the wordplay.
'return of' is a reversal indicator.
'one' becomes 'an' (an apple is one apple).
'shut in cooler' becomes 'if' (I can't explain this - if you can you should believe this answer much more).
'an' written backwards gives 'na'.
'na'+'if'='NAIF'
'an' acts as a link.
Can you help me to learn more?
(Other definitions for naif that I've seen before include "Artless" , "Inexperienced" , "Unsophisticated" , "unaffected simplicity" , "Green" .)