Some dozens ignoring a flag (6)
I believe the answer is:
ensign
'flag' is the definition.
(I know that ensign is a type of flag)
'some dozens ignoring a' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ENSIGN' can be found hidden inside 'dozens ignoring a'.
(Other definitions for ensign that I've seen before include "Flag; standard-bearer" , "Standard - flag" , "SECOND PART OF 10" , "Flags flown by a ship to show its nationality" , "Junior US naval officer" .)