Mark as important (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
flag
'mark as important' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for flag that I've seen before include "Colours - become tired" , "National standard" , "Droop; iris" , "National emblem; tire" , "Item of bunting" .)