Allowance involves old Treasury leader spinning (8)
I believe the answer is:
rotation
'spinning' is the definition.
(thesaurus)
'allowance involves old treasury leader' is the wordplay.
'allowance' becomes 'ration' (I've seen this before).
'involves' indicates putting letters inside.
'leader' suggests taking the first letters.
The initial letters of 'old treasury' is 'ot'.
'ration' going around 'ot' is 'ROTATION'.
(Other definitions for rotation that I've seen before include "Turn of a wheel" , "Going round" , "Turning movement around an axis" , "Revolutionary movement" , "altering of crops" .)