@akronius
Look at the second chart on the Wikipedia page you used.
八 "Hachi" + 百 "Hyaku = "Happyaku" or 800
八 "Hachi" + 千 "Sen" = "Hassen" or 8,000
So 八 "Hachi" can be shortened to just "Ha".
"Ha" is one of the special kana in Japanese, it has both a "voiced" and "half-voiced" version.
は...