Old flour supplier Will keeps changing mind (8)
I believe the answer is:
windmill
'old flour supplier' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'will keeps changing mind' is the wordplay.
'keeps' means one lot of letters goes inside another.
'changing' is an anagram indicator.
'mind' with letters rearranged gives 'indm'.
'will' placed around 'indm' is 'WINDMILL'.
Can you help me to learn more?
(Other definitions for windmill that I've seen before include "Rotating toy" , "Don Quixote tilted at one, thinking it a dragon" , "Source of green power" , "Natural energy generator" , "Air-driven device" .)