Easily handled in vast, endlessly vague domain (4,4)
I believe the answer is:
grey area
'vague domain' is the definition.
(I've seen this before)
'easily handled in vast endlessly' is the wordplay.
'easily handled' becomes 'yare' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'vast' becomes 'great' (I've seen this in another clue).
'endlessly' means to remove the last letter.
'great' with its final letter taken off is 'grea'.
'yare' inserted into 'grea' is 'GREY AREA'.
Can you help me to learn more?
(Other definitions for grey area that I've seen before include "Matter about which there is no certainty" , "Woolly matter" , "doubtful situation" , "What many pensioners have upstairs" , "where work is inadequate" .)