Vigilant dealer taking part (5)
I believe the answer is:
alert
'vigilant' is the definition.
(similar in meaning)
'dealer taking part' is the wordplay.
'part' indicates a hidden word.
'ALERT' is hidden within 'dealer taking'.
(Other definitions for alert that I've seen before include "On one's toes" , "Intellectually active" , "Wakeful, observant" , "Wide awake and watchful" , "On the ball" .)