Fear wife's stuck in casualty (3)
I believe the answer is:
awe
'fear' is the definition.
(awe is a kind of fear)
'wife's stuck in casualty' is the wordplay.
'wife' becomes 'w'.
'stuck in' is an insertion indicator.
'casualty' becomes 'ae' (abbreviation for Accident and Emergency).
'w' inserted within 'ae' is 'AWE'.
(Other definitions for awe that I've seen before include "Wide-eyed wonder" , "Great dread" , "Reverential feeling" , "Scots lock [LOCH??]" , "Wonder, reverence" .)