IPA: /ˈflæɡər/
KK: /ˈflæɡər/
A person who uses signs or flags to guide vehicles and pedestrians safely around construction areas or other hazards.
The flagger stood at the roadblock, waving a bright flag to direct the cars.
The word 'flagger' is derived from 'flag' (from Old Norse *flagg*, meaning a piece of cloth or banner) and '-er' (meaning a person who). A flagger is a person who uses or displays a flag, often in a signaling context.
Think of a person who uses a 'flag' — the '-er' indicates that this person is associated with the action of displaying or using a flag.