Collect a cold cure concoction (6)
I believe the answer is:
accrue
'collect' is the definition.
(to accrue is to collect or gather)
'a cold cure concoction' is the wordplay.
'cold' becomes 'c' (eg on taps).
'concoction' indicates an anagram.
'cure' with letters rearranged gives 'crue'.
'a'+'c'+'crue'='ACCRUE'
(Other definitions for accrue that I've seen before include "Fall due; accumulate" , "(Of money) build up by regular receipts" , "Grow like interest on capital" , "Grow like interest on money" , "Allow for (charge) at end of accounting period" .)