National emblem that's terrifying on lieutenant's face (4)
I believe the answer is:
leek
'national emblem' is the definition.
(I've seen this before)
'terrifying on lieutenant's face' is the wordplay.
'terrifying' becomes 'eek' (I am not sure about this - if you are sure you should believe this answer much more).
'on' says to put letters next to each other.
'face' says to take the initial letters.
The first letter of 'lieutenants' is 'l'.
'eek' after 'l' is 'LEEK'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for leek that I've seen before include "Vegetable associated with Wales" , "Plant (onion relative) eaten as a vegetable" , "Welsh national symbol" , "Eat the vegetable and keel over" , "Green and white vegetable" .)