Artillery regiment with gun elevated in routine (7)
I believe the answer is:
regular
'routine' is the definition.
(similar in meaning)
'artillery regiment with gun elevated' is the wordplay.
'artillery regiment' becomes 'RA' (Royal Artillery).
'with' is a charade indicator (letters next to each other).
'gun' becomes 'luger' (type of pistol).
'elevated' is a reversal indicator (in a down clue, letters go up).
'ra'+'luger'='raluger'
'raluger' reversed gives 'REGULAR'.
'in' acts as a link.
(Other definitions for regular that I've seen before include "'Steady, uniform (7)'" , "Frequent - usual" , "Ordinary" , "fighter" , "At set intervals" .)