Resistant to alcoholic strength (5)
I believe the answer is:
proof
I believe this clue is a double definition.
'resistant' is the first definition.
(thesaurus)
'alcoholic strength' is the second definition.
(I've seen this in another clue)
'to' acts as a link.
(Other definitions for proof that I've seen before include "Body of evidence" , "Mathematical argument" , "a writer may check" , "Draft copy of printed text" , "Clear evidence" .)