I appreciate that Lucy oddly selected bathroom powder (4)
I believe the answer is:
talc
'bathroom powder' is the definition.
(I've seen this in another clue)
'i appreciate that lucy oddly selected' is the wordplay.
'i appreciate that' becomes 'ta' (informal way of saying thank you).
'oddly selected' means one should take alternating letters.
The alternate letters of 'lucy' are 'lc'.
'ta'+'lc'='TALC'
(Other definitions for talc that I've seen before include "I may dust" , "Scented powder used after bathing" , "After-bath powder" , "Drier" , "White powder for the bathroom" .)