Conventional flag (8)
I believe the answer is:
standard
I believe this is a double definition.
'conventional' is the first definition.
(I've seen this before)
'flag' is the second definition.
(standard is a kind of flag)
(Other definitions for standard that I've seen before include "Flag - accepted level" , "Principle" , "'Reference point, touchstone (8)'" , "Guide-line" , "Against which to measure the rest" .)