The Parisian Complaint Unit (6)
I believe the answer is:
league
'unit' is the definition.
(league is a kind of unit)
'the parisian complaint' is the wordplay.
'the parisian' becomes 'le' (definite article in French).
'complaint' becomes 'ague' (ague is a kind of disease**).
'le'+'ague'='LEAGUE'
(Other definitions for league that I've seen before include "Association of teams for competition" , "Group of teams competing over a period" , "Former measure of distance, usually about three miles" , "About five kilometres" , "Alliance - three (poetic) miles" .)