Understanding French in shelter ultimately possible (7)
I believe the answer is:
entente
'understanding' is the definition.
(an entente is an alliance or understanding)
'french in shelter ultimately possible' is the wordplay.
'french in' becomes 'en' (French for 'in').
'shelter' becomes 'tent' (canvas shelter).
'ultimately' indicates one should take the final letters.
The final letter of 'possible' is 'e'.
'en'+'tent'+'e'='ENTENTE'
(Other definitions for entente that I've seen before include "Interstate understanding" , "Teen ten involved in friendly understanding between countries" , "Agreement between governments" , "Diplomatic agreement" , "Friendly alliance between states" .)