Dealer tries to keep vigilant (5)
I believe the answer is:
alert
'vigilant' is the definition.
(similar in meaning)
'dealer tries to keep' is the wordplay.
'to keep' says the answer is hidden in the clue.
'ALERT' is hidden in the letters of 'dealer tries'.
(Other definitions for alert that I've seen before include "Intellectually active" , "Quick to notice" , "On the ball" , "'Attentive, vigilant (5)'" , "Wakeful, observant" .)