Fill up ten churns — that's ample (9)
I believe the answer is:
plentiful
'that's ample' is the definition.
(synonyms)
'fill up ten churns' is the wordplay.
'churns' indicates an anagram (I've seen 'churning' mean this).
'fill'+'up'+'ten'='fillupten'
'fillupten' with letters rearranged gives 'PLENTIFUL'.
(Other definitions for plentiful that I've seen before include "Productive" , "Abundant, copious" , "Abundant - profuse" , "Existing in great quantities" , "common" .)