EinER

Einer is a German word that centers on the notions of "one" and "one person." In contemporary usage it functions primarily as a pronoun and appears in constructions that refer to a single person within a group, such as one of them: e.g., einer von ihnen (one of them) or einer von uns (one of us). It can also serve as a stand-alone indefinite pronoun meaning "someone" in informal or literary contexts, as in Da ist einer an der Tür (There is someone at the door).

As a pronoun, einer is part of a family of forms that reflects gender and case in German grammar; the exact form changes with the grammatical role in a sentence. A common, widely used sense is to designate a single member of a known set or to indicate an unspecified person in a general sense.

Etymology and cognates: einer derives from the Old High German einar, related to the Proto-Germanic root ainaz meaning "one." It is cognate with the English word one and with Dutch een, reflecting the shared Germanic heritage of the word.

Related usage: the word appears in fixed phrases and compounds, most notably in the compound eins meaning the numeral one, or in expressions that specify distribution among a group (einerseits, andererseits, while not all forms are interchangeable with the standalone pronoun). In formal writing, genau which form of eins, einer, or eine is appropriate depends on number, gender, and case.

Overall, einer remains a concise, flexible term in German for signaling a single, non-specific or particular member of a set, with its sense shaped by grammatical context.