Panic contained by Territorial Army (5)

I believe the answer is:

alarm

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'panic' is the definition.
(alarm can mean panic or fear)

'contained by territorial army' is the wordplay.
'ALARM' is hidden in amongst the letters.
But, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for alarm that I've seen before include "Trepidation" , "Warning of danger" , "Scare with warning device" , "Frighten, disturb" , "Frighten, scare" .)

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