Poetic tat about undergarment (9)
I believe the answer is:
petticoat
'undergarment' is the definition.
(I know that petticoat is a type of undergarment)
'poetic tat about' is the wordplay.
'about' indicates an anagram.
'poetic'+'tat'='poetictat'
'poetictat' with letters rearranged gives 'PETTICOAT'.
(Other definitions for petticoat that I've seen before include "Slip" , "Woman's underskirt" , "Female undergarment" , "Woman's undergarment" , "London Lane" .)