One peculiar feature of the Danish language is that the numerals 50, 60, 70, 80 and 90 are (as are the French numerals from 80 through 99) based on a vigesimal system, meaning that the score (20) is used as a base unit in counting. "Tres" (short for "tre-sinds-tyve", "three times twenty") means 60, while 50 is "halvtreds" (short for "halvtredje-sinds-tyve", "half third times twenty", implying two score plus half of the third score). The ending "sindstyve" meaning "times twenty" is no longer included in cardinal numbers, but may still be used in ordinal numbers. Thus, in modern Danish fifty-two is usually rendered as "tooghalvtreds" from the now obsolete "tooghalvtredsindstyve", whereas 52nd is either "tooghalvtredsende" or "tooghalvtredsindstyvende". Twenty is "tyve" (derived from Old Danish "tiughu", a haplology of "tuttiughu", meaning 'two tens'), while thirty is "tredive" (Old Danish "þrjatiughu", "three tens"), and forty is "fyrre" (Old Danish "fyritiughu", "four tens", still used today as the archaism "fyrretyve"). Thus, the suffix "-tyve" should be understood as a plural of "ti" (10), though to modern Danes "tyve" means 20, making it hard to explain why "fyrretyve" is 40 (four tens) and not 80 (four twenties).