Lowering of Parisian somewhere below ground (10)
I believe the answer is:
debasement
'lowering' is the definition.
(debasing oneself)
'of parisian somewhere below ground' is the wordplay.
'of parisian' becomes 'de' ('of' in French).
'somewhere below ground' becomes 'basement' (area below a building).
'de'+'basement'='DEBASEMENT'
(Other definitions for debasement that I've seen before include "Degradation" , "What's lowering" , "Dishonour" .)