Dead wrong about the tango being old-fashioned (5)
I believe the answer is:
dated
'old-fashioned' is the definition.
(thesaurus)
'dead wrong about the tango' is the wordplay.
'wrong' indicates anagramming the letters.
'about' means one lot of letters goes inside another.
'the tango' becomes 't' (phonetic alphabet: alpha, bravo, charlie etc.).
'dead' anagrammed gives 'daed'.
'daed' enclosing 't' is 'DATED'.
'being' acts as a link.
(Other definitions for dated that I've seen before include "Revealed the age of" , "Walked out with" , "Old fashioned" , "Old-fashioned" , "No longer fashionable or current" .)