Custodian's ringful (4)
I believe the answer is:
keys
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">custodian's ringful</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for keys that I've seen before include "Lock-openers?" , "Islands; piano parts" , "Low islands, sycamore fruits" , "Solutions" , "Bunch of openers?" .)