Royal guardsman taking out the French from parapet openings (7)
I believe the answer is:
porthos
'royal guardsman' is the definition.
(reference to The Three Musketeers)
'the french from parapet openings' is the wordplay.
'the french' becomes 'le'.
'from' is a deletion indicator.
'parapet openings' becomes 'portholes'.
'portholes' with 'le' taken away is 'PORTHOS'.
'taking out' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
(Other definitions for porthos that I've seen before include "Soldier character" , "Colleague of Athos, Aramis" , "French soldier" , "One of Three Musketeers" , "Literary musketeer" .)