One spelt with a choice of letters? (4)
I believe the answer is:
word
'one spelt' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'with a choice of letters?' is the wordplay.
'with' becomes 'w' (short for with).
'a choice of letters?' becomes 'ord' (I can't explain this - if you can you should give a lot more credence to this answer).
'w'+'ord'='WORD'
Can you help me to learn more?
(Other definitions for word that I've seen before include "See 21" , "Message" , "The Bible is the . . . . of God" , "Brief statement" , "Statement; signal" .)