It's useful for sleeping out, perhaps, in part of Tufnell Park (5)
I believe the answer is:
futon
'park' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'it's useful for sleeping out perhaps in part of tufnell' is the wordplay.
I cannot quite see how this works, but
'for' could be 'to' (eg both can mean 'in the opinion of') and 'to' is present in the answer.
The remaining letters 'fun' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for futon that I've seen before include "Foldable mattress" , "A Japanese folding bed-chair" , "Japanese couch-bed convertible" , "Padded unsprung mattress" , "Japanese quilted mattress used as bed" .)