Dealer essentially provides weapons for spooks (6)
I believe the answer is:
alarms
'spooks' is the definition.
(I've seen this in another clue)
'dealer essentially provides weapons' is the wordplay.
'essentially' indicates the central letters.
'provides weapons' becomes 'arms' (I've seen this in another clue).
The middle letters of 'dealer' are 'al'.
'al'+'arms'='ALARMS'
'for' is the link.
(Other definitions for alarms that I've seen before include "Clocks that wake sleepers" , "Warning sounds" , "Scares, hopefully burglars" , "Puts on guard or frightens" , "Devices to signal danger" .)