Tin makes alloy wrong (8)
I believe the answer is:
mistaken
'wrong' is the definition.
(I know that wrong can be written as mistaken)
'tin makes alloy' is the wordplay.
'alloy' is an anagram indicator.
'tin'+'makes'='tinmakes'
'tinmakes' is an anagram of 'MISTAKEN'.
(Other definitions for mistaken that I've seen before include "Wrong in opinion, judgment etc." , "Wrong (in judgement)" , "Wrong-headed" , "'Wrong, misguided (8)'" , "Wrongly understood" .)