Ruin some poor Frenchman (8)
I believe the answer is:
monsieur
'frenchman' is the definition.
(I've seen this before)
'ruin some poor' is the wordplay.
'poor' indicates an anagram.
'ruin'+'some'='ruinsome'
'ruinsome' is an anagram of 'MONSIEUR'.
(Other definitions for monsieur that I've seen before include "Frenchman" , "A French mister" , "French title of respect" , "He's French" , "French gentleman" .)