Keep solid case for ring (5)
I believe the answer is:
hoard
'keep' is the definition.
(thesaurus)
'solid case for ring' is the wordplay.
'solid' becomes 'hard' ('hard' can be similar in meaning to 'solid').
'case for' means one lot of letters goes inside another.
'ring' becomes 'o'.
'hard' enclosing 'o' is 'HOARD'.
(Other definitions for hoard that I've seen before include "Accumulated store" , "Secret stash" , "Hidden stock" , "Secret store of valuables" , "Accumulate" .)