Difficult to hide ring in collection (5)
I believe the answer is:
hoard
'collection' is the definition.
(I've seen this before)
'difficult to hide ring' is the wordplay.
'difficult' becomes 'hard' (associated in meaning).
'to hide' indicates putting letters inside.
'ring' becomes 'o'.
'hard' going around 'o' is 'HOARD'.
'in' is the link.
(Other definitions for hoard that I've seen before include "Rhoda (anag.)" , "Squirrel away" , "Store of money or valuables" , "Valuable store" , "Accumulate" .)