Attempts to frighten the soldier that’s guarding (7)
I believe the answer is:
threats
'attempts to frighten' is the definition.
I can't judge whether this defines the answer.
'soldier that's guarding' is the wordplay.
'soldier' becomes 're' (Royal Engineer).
'guarding' means one lot of letters goes inside another.
're' going into 'thats' is 'THREATS'.
'the' is the link.
Can you help me to learn more?
(Other definitions for threats that I've seen before include "Statements of intentions to harm" , "Sources of danger -- shatter (anag)" , "Menacing statements" , "Terrifying demands" , "Shatter (anag) - menaces" .)