Genuine gold, subsequently acquiring twitch (9)
I believe the answer is:
authentic
'genuine' is the definition.
(similar in meaning)
'gold subsequently acquiring twitch' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'subsequently' becomes 'then' (synonyms).
'acquiring twitch' becomes 'tic' (I can't explain this - if you can you should believe this answer much more).
'au'+'then'+'tic'='AUTHENTIC'
Can you help me to learn more?
(Other definitions for authentic that I've seen before include "reliable" , "Genuine, not a copy" , "Real, genuine" , "trustworthy" , "Bona fide" .)