dein

Dein is a German possessive determiner meaning "your" when addressing someone informally. It accompanies a noun and changes form to agree with the noun’s gender, number, and case. The form is used with singular informal "you" and contrasts with the formal possessive "Ihr" used in polite addresses. In everyday language, dein appears in phrases such as dein Haus, deine Ideen, or deinen Kaffee.

Declension: The endings follow the pattern of other possessive determiners. For example: nominative—masculine dein, feminine deine, neuter dein, plural deine; accusative—masculine deinen, feminine deine, neuter dein, plural deine; dative—masculine deinem, feminine deiner, neuter deinem, plural deinen; genitive—masculine deines, feminine deiner, neuter deines, plural deiner. The determiner is placed before the noun, and the noun may show its own endings if required by grammar.

Usage notes: Dein is used with people you know well, such as friends, family, or peers. With strangers or in professional contexts, the formal Ihr is appropriate. Dein forms are taught early in German language learning and are essential for expressing ownership in everyday speech.

Etymology and related forms: Dein belongs to the Germanic family of possessive determiners, with cognates in other West Germanic and Nordic languages, such as Dutch jouw, Norwegian din, and Icelandic þinn. Its development traces back to demonstrative forms that evolved into possessive adjectives and pronouns over time. In modern usage, dein is a standard informal alternative to the formal possessive.