Regular soldiers put November in events book (8)
I believe the answer is:
Here is my best explanation:
'regular' is the definition.
'soldiers put november in events book' is the subsidiary indication.
'soldiers put' becomes 'or' (I can't justify this - if you can you should believe this answer much more).
'november' becomes 'n' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' is an insertion indicator.
'events book' becomes 'diary'.
'n' going into 'diary' is 'dinary'.
(Other definitions for ordinary that I've seen before include "Everyday", "Not worthy of noting in X-Files", "simple charge", "Unremarkable", "standard", "Common", "charge for arms", "Run-of-the-mill", "Standard" and "Not exceptional in any way".)