Shock at almost being bitten (4)
I believe the answer is:
stun
'shock' is the definition.
('stun' can be a synonym of 'shock')
'almost being bitten' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'being bitten' becomes 'stung' ('stung' can be a synonym of 'bitten').
'stung' with its last letter removed is 'STUN'.
'at' acts as a link.
(Other definitions for stun that I've seen before include "Make senseless or dizzy with a blow" , "Render temporarily senseless" , "Knock out temporarily" , "Render unconscious" , "Anaesthetise" .)