Discouragement from French shelter - stray inside (9)
I believe the answer is:
deterrent
'discouragement' is the definition.
(I've seen this before)
'from french shelter stray inside' is the wordplay.
'from french' becomes 'de' ('from' in French).
'shelter' becomes 'tent' (canvas shelter).
'stray' becomes 'err' (to err is to stray or go wrong).
'inside' indicates putting letters inside.
'tent' placed around 'err' is 'terrent'.
'de'+'terrent'='DETERRENT'
(Other definitions for deterrent that I've seen before include "Discouragement, disincentive" , "Tending to put off" , "Nuclear weapons allegedly" , "Something intended to discourage" , "Eg, a nuclear weapon" .)