Involved ales in solution (6)
I believe the answer is:
saline
'solution' is the definition.
(chemical solution)
'involved ales in' is the wordplay.
'involved' indicates anagramming the letters (involved can mean confusing or complex).
'ales'+'in'='alesin'
'alesin' with letters rearranged gives 'SALINE'.
(Other definitions for saline that I've seen before include "solution" , "Like seawater" , "Intravenous feeding" , "Like contents of cellar" , "Containing or tasting of salt" .)