Awkward matter, but useful for angler (3,2,5)
I believe the answer is:
can of worms
'matter but useful for angler' is the definition.
'can of worms' can be an answer for 'matter' (thesaurus). I'm not certain of the 'but useful for angler' bit.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for can of worms that I've seen before include "an angler might have?" , "Opening this could be problem" , "Bird's convenience food" , "this may turn out awkward" , "What may prove problematic" .)