Ready with small collections (4)
I believe the answer is:
sets
'collections' is the definition.
(set is a kind of collection)
'ready with small' is the wordplay.
'ready' becomes 'set' (set can mean ready or prepared).
'with' says to put letters next to each other.
'small' becomes 's' (abbreviation - e.g. clothes size).
'set'+'s'='SETS'
(Other definitions for sets that I've seen before include "Solidifies" , "Scenery etc. of dramatic productions" , "Scenery etc. of 11 across productions" , "Classes" , "Major divisions of tennis match" .)