A way into free flight (8)
I believe the answer is:
aviation
'flight' is the definition.
(thesaurus)
'a way into free' is the wordplay.
'way' becomes 'via' (I've seen this in other clues**).
'free' indicates anagramming the letters.
'into' anagrammed gives 'tion'.
'a'+'via'+'tion'='AVIATION'
(Other definitions for aviation that I've seen before include "The practice or science of flying aircraft" , "The business of airlines" , "Flying in general" , "Aircraft operating business" , "The aircraft industry" .)