Alien son emptied boxes despite what mom said (8)
I believe the answer is:
spaceman
'alien' is the definition.
(thesaurus)
'son emptied boxes despite what mom said' is the wordplay.
I cannot really see how this works, but
'son' could be 's' (genealogical abbreviation for son) and 's' is found in the answer.
'mom' could be 'ma' (synonyms) and 'ma' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for spaceman that I've seen before include "Armstrong, perhaps?" , "Armstrong, say" , "NASA PC, me! (anag)" , "Out-of-this-world chap?" , "one requiring a supply of oxygen?" .)