Alien saying about refuse (5)
I believe the answer is:
waste
'refuse' is the definition.
(I know that refuse can be written as waste)
'alien saying about' is the wordplay.
'alien' becomes 'et' (extra terrestrial).
'saying' becomes 'saw' (saw is a kind of saying).
'about' says the letters should be written in reverse.
'et'+'saw'='etsaw'
'etsaw' back-to-front is 'WASTE'.
(Other definitions for waste that I've seen before include "Use inefficiently or inappropriately" , "Detritus" , "Fail to use (profitably)" , "Spend thoughtlessly or use inefficiently" , "desert" .)