National army's hiding fear (5)
I believe the answer is:
alarm
'fear' is the definition.
(alarm is a kind of fear)
'national army's hiding' is the wordplay.
'hiding' indicates a hidden word.
'ALARM' can be found hidden inside 'national armys'.
(Other definitions for alarm that I've seen before include "Unnerve" , "Trepidation" , "Consternation: kind of clock" , "with which many awake to in the morning" , "Anxious awareness of danger" .)