Aliens odd solution (6)
I believe the answer is:
saline
'solution' is the definition.
(chemical solution)
'aliens odd' is the wordplay.
'odd' is an anagram indicator.
'aliens' anagrammed gives 'SALINE'.
(Other definitions for saline that I've seen before include "solution" , "Like contents of cellar" , "Salty to aliens" , "Intravenous feeding" , "Containing salt or salts" .)