Using attic, poet changed undergarment (9)
I believe the answer is:
petticoat
'changed undergarment' is the definition.
'petticoat' can be an answer for 'undergarment' (petticoat is a kind of undergarment). I'm not certain of the 'changed' bit.
'using attic poet' is the wordplay.
'using' indicates anagramming the letters (the letters used in a different way).
'attic'+'poet'='atticpoet'
'atticpoet' is an anagram of 'PETTICOAT'.
Can you help me to learn more?
(Other definitions for petticoat that I've seen before include "garment" , "Slip" , "Woman's undergarment" , "Woman's underskirt" , "Female undergarment" .)