Unusual spite shown to the French in a letter (7)
I believe the answer is:
epistle
'letter' is the definition.
(I know that letter can be written as epistle)
'unusual spite shown to the french' is the wordplay.
I cannot really see how this works, but
an anagram of 'spite' is 'epist' which is located in the answer.
'the french' could be 'le' ('the' in French) and 'le' is found within the answer.
No letters remain.
This explanation may well be incorrect...
'in a' is the link.
Can you help me to learn more?
(Other definitions for epistle that I've seen before include "A letter from St Paul" , "Pets lie (anag)" , "A letter, biblical perhaps" , "may be written off" , "Long formal letter (found in the New Testament?)" .)