The word "us" has a direct lineage from Old English "ūs," which served the same grammatical function. This Old English form descended from the Proto-Germanic "uns," and further back from the Proto-Indo-European "n̥s-," "nos-," the accusative form of the first-person plural pronoun. The journey from Proto-Indo-European to modern English showcases a consistent preservation of its core function as an object pronoun, with the phonetic form simplifying over millennia from "nos" to "us." Its meaning has remained stable, representing the speaker plus others in the position of a grammatical object.

This is a simplex word. It is the objective case form of the first-person plural pronoun "we." Its functional role is purely grammatical, serving as an object pronoun in English.