the Nikkei indexNik·kei in·dex, the /ˌnɪkeɪ ˈɪndeks/ (also the Nikkei, the Nikkei Average) a number that shows how well or badly shares have performed on the Tokyo stock exchange on a particular day. The number is based on the share prices of about 200 important companies. → see also Dow Jones Average, FT 100 Share Index, the, Hang Seng Index, the