íónum

þínum is a form of the Icelandic possessive determiner meaning “your.” It is used to indicate ownership with a noun in the dative case and is part of the inflectional system that marks number and gender of the possessed noun rather than the possessor.

In Icelandic, possessive determiners decline to agree with the noun they modify. The dative form such as þínum appears in contexts where the governed noun is in the dative, often after prepositions or with verbs that require the dative. For example, after a preposition like með (with), one can encounter phrases such as með þínum vinum (“with your friends”). The form thus functions as a marker of both possession and case.

The form þínum is related to other mood and case forms of the same determiner, which have distinct appearances in nominative and other cases (for example, the nominative forms such as þinn, þín, or þitt, used before subjects or predicates). The exact form of the possessive determiner shifts with number (singular vs. plural) and gender of the possessed noun, as is typical for Icelandic possessive adjectives and determiners.

Etymology traces þínum to the Icelandic word for “your,” itself deriving from older North Germanic and Old Norse forms that developed into the modern Icelandic system of inflected possessives. The form aligns with comparable possessive constructions across the North Germanic languages.

See also: Icelandic grammar, possessive determiners, Icelandic case system.