Enjoy welcoming knight who French let go (10)
I believe the answer is:
relinquish
'let go' is the definition.
(thesaurus)
'enjoy welcoming knight who french' is the wordplay.
'enjoy' becomes 'relish' (synonyms).
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'knight' becomes 'N' (chess abbreviation).
'who french' becomes 'qui' ('who' in French).
'n'+'qui'='nqui'
'relish' going around 'nqui' is 'RELINQUISH'.
(Other definitions for relinquish that I've seen before include "Give up - let go" , "Surrender" , "Drop" , "Abandon" .)