Slack-jawed feeling (3)
I believe the answer is:
awe
'slack-jawed feeling' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for awe that I've seen before include "Great dread" , "Scots lock [LOCH??]" , "Reverent fear" , "Amazed wonder" , "Wondrous fear" .)