Attractively thin person posting letter with pounds inside (7)
I believe the answer is:
slender
'attractively thin' is the definition.
'slender' can be an answer for 'thin' (synonyms). I am not sure about the 'attractively' bit.
'person posting letter with pounds inside' is the wordplay.
I cannot quite understand how this works, but
'person' could be 'lender' (lender is a kind of person) and 'lender' is found in the answer.
'letter' could be 's' and 's' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for slender that I've seen before include "Svelte" , "Slight in form" , "Lean" , "Slight, slim" , "short of a pound or two of flesh?" .)