Group ready (3)
I believe the answer is:
set
This clue is a double definition.
'group' is the first definition.
(both can mean a collection)
'ready' is the second definition.
(set can mean ready or prepared)
(Other definitions for set that I've seen before include "'Put, place or fix in position (3)'" , "exclusive party" , "Create a puzzle" , "Put, coagulate" , "Fix in place; similar group" .)