Gold seen in mart could be shock (6)
I believe the answer is:
trauma
'shock' is the definition.
(I've seen this before)
'gold seen in mart could be' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'seen in' is an insertion indicator.
'could be' indicates anagramming the letters.
'mart' with letters rearranged gives 'trma'.
'au' going into 'trma' is 'TRAUMA'.
(Other definitions for trauma that I've seen before include "Emotional upset" , "Deep distress; injury" , "Psychological 23" , "Deeply distressing or disturbing experience" , "Nervous shock" .)