Awakening, missing start of drinking party (7)
I believe the answer is:
arousal
'awakening' is the definition.
(I've seen this in another clue)
'missing start of drinking party' is the wordplay.
'missing start of' means to remove the first letter.
'drinking party' becomes 'carousal' (I've seen this before).
'carousal' with its first letter taken off is 'AROUSAL'.
(Other definitions for arousal that I've seen before include "Awakening (of emotion, etc)" , "heating?" , "Drinking spree" , "Act of waking (someone)" , "Act of awakening" .)