Understanding this should be mixed with gin (7)
I believe the answer is:
'understanding' is the definition.
(insight is a kind of understanding)
'this should be mixed with gin' is the wordplay.
'should be mixed with' indicates anagramming the letters.
'this' anagrammed with 'gin' makes 'INSIGHT'.
(Other definitions for insight that I've seen before include "Penetrative quality" , "Awareness" , "Deep understanding" , "what psychoanalysts hope to gain" , "Sudden understanding" .)