Letter that is spelt badly (7)
I believe the answer is:
epistle
'letter' is the definition.
(I know that letter can be written as epistle)
'is spelt badly' is the wordplay.
I cannot really see how this works, but
'is' is within the answer.
This explanation may well be incorrect...
'that' acts as a link.
Can you help me to learn more?
(Other definitions for epistle that I've seen before include "screed" , "extract of the Bible" , "A letter - as from Apostle?" , "(E.g. Paul's) letter" , "may be written off" .)