Least wise place to keep eggs (7)
I believe the answer is:
inanest
'least wise' is the definition.
(inane is the opposite of wise)
'place to keep eggs' is the wordplay.
'place' becomes 'nest' (I have seen 'Place of retreat' mean 'nest' so perhaps 'place' could also mean 'nest').
'to' says to put letters next to each other (I've seen this in other clues).
'keep eggs' becomes 'ina' (I can't explain this - if you can you should believe this answer much more).
'nest' after 'ina' is 'INANEST'.
(Other definitions for inanest that I've seen before include "most senseless" , "Exhibiting minimal sense" , "Most stupid" , "Most silly" , "Most cuckoo" .)