Name ultimately I spelt wrong in letter (7)
I believe the answer is:
epistle
'letter' is the definition.
(epistle is a kind of letter)
'name ultimately i spelt wrong' is the wordplay.
'ultimately' says to take the final letters.
'wrong' indicates anagramming the letters.
The last letter of 'name' is 'e'.
'i'+'spelt'='ispelt'
'ispelt' with letters rearranged gives 'pistle'.
'e'+'pistle'='EPISTLE'
'in' is the link.
(Other definitions for epistle that I've seen before include "A letter, biblical perhaps" , "A letter from St Paul" , "Biblical missive" , "Long formal letter (found in the New Testament?)" , "Pets lie (anag)" .)