Gunners with gun elevated in routine (7)
I believe the answer is:
regular
'routine' is the definition.
(similar in meaning)
'gunners with gun elevated' is the wordplay.
'gunners' becomes 'RA' (Royal Artillery).
'with' says to put letters next to each other.
'gun' becomes 'luger' (type of pistol).
'elevated' says the letters should be written backwards (in a down clue, letters go up).
'ra'+'luger'='raluger'
'raluger' backwards is 'REGULAR'.
'in' acts as a link.
(Other definitions for regular that I've seen before include "Steady, even" , "Soldier - uniform" , "In accordance with a fixed order" , "'Steady, uniform (7)'" , "One present often" .)