Free translation of tag, sir (6)
I believe the answer is:
gratis
'free' is the definition.
(I know that free can be written as gratis)
'translation of tag sir' is the wordplay.
'translation of' is an anagram indicator (I've seen this in other clues).
'tag'+'sir'='tagsir'
'tagsir' is an anagram of 'GRATIS'.
(Other definitions for gratis that I've seen before include "Without charge" , "Free (Latin)" , "Free of charge" , "Free, at no cost" , "Without payment" .)