1. noun Clothing, especially a vest or jacket, made from highly reflective materials or containing bright, vivid colors. A shortening of "high visibility (clothing)." Sometimes hyphenated. Primarily heard in UK, Ireland. There are no street lamps along that road, so I always carry a torch and wear my hi vis when I go walking along it at night. Take a couple high-vises with you and make sure everyone on the crew is wearing one.
2. adjective Of, containing, or made of such highly visible materials or colors. Usually hyphenated and used before a noun. Primarily heard in UK, Ireland. Please make sure you wear your high-vis vest when you ride your bicycle in the dark! All workers are required to wear hi-vis helmets and jackets while on site.
See also: vi