ordinal number

1. A word that expresses the relative position of an item in a sequence.

   First, second and third are the ordinal numbers corresponding to one, two and three.

2. A natural number used to denote position in a sequence.

   In the expression a₃, the "3" is an ordinal number.

   Ordnungszahl, Ordnungszahlwort, Ordinale

   поря́дковое числи́тельноеporjádkovoje čislítelʹnoje, поря́дковый но́мерporjádkovyj nómer, но́мерnómer

   the number designating place in an ordered sequence

3. Such a number generalised to correspond to any cardinal number (the size of some set); formally, the order type of some well-ordered set of some cardinality a, which represents an equivalence class of well-ordered sets (exactly those of cardinality a) under the equivalence relation "existence of an order-preserving bijection".

1. Eight hundredth, nine hundredth and one thousandth are ordinal numbers.

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2. One is a cardinal number; first is an ordinal number.

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3. Some countries use ordinal numbers to count millennia, whereas others count them using cardinal numbers.

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regular