Purpose of French band taking circuitous route (10)
I believe the answer is:
meandering
'taking circuitous route' is the definition.
'purpose of french band' is the wordplay.
'purpose' becomes 'mean' (I've seen this before).
'of french' becomes 'de'.
'band' becomes 'ring' ('ring' can be a synonym of 'band').
'mean'+'de'+'ring'='MEANDERING'
(Other definitions for meandering that I've seen before include "Digressive" , "convoluted" , "Aimlessly wandering" , "not in straight line" , "Serpentine?" .)