Eins
Eins is the German cardinal number for one. It denotes a single unit and is used when counting or identifying the first item in a set, as in the sequence eins, zwei, drei. Unlike the indefinite article ein, which accompanies a noun, eins can function as a standalone substantive when the noun is omitted, for example Ich nehme eins.
Beyond simple counting, eins appears in common phrases and expressions. One-to-one is expressed as eins zu eins,
Etymology and cognates: eins derives from the Proto-Germanic stem ainaz, related to the English word one and
See also: numbers in German, German grammar, numeral usage, counting in German.
Note: The term eins is distinct from the indefinite article ein; eins is used when counting or