Panic in the manner of fighting corps (5)
I believe the answer is:
alarm
'panic' is the definition.
(thesaurus)
'in the manner of fighting corps' is the wordplay.
'in the manner of' becomes 'ala' ('a la' means 'in the manner of', as in 'a la mode').
'fighting corps' becomes 'rm' (abbreviation for Royal Marines).
'ala'+'rm'='ALARM'
(Other definitions for alarm that I've seen before include "Warning bell" , "Clock that wakes the sleeper" , "Device to signal danger" , "with which many awake to in the morning" , "Warning of danger" .)