Man? And what one isn't, it's said (6)
I believe the answer is:
island
'man?' is the definition.
(man is a kind of island)
'what one isn't it's said' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'and' is the link.
Can you help me to learn more?
(Other definitions for island that I've seen before include "Pedestrian area in middle of road crossing" , "Water-girt territory" , "See 13" , "Boffin, Baffin or Bali, say" , "Body of land entirely surrounded by water" .)