Yeah, I made that genitive up, but only to describe a real phenomenon in Latin! Some adjectives of likeness, nearness, and belonging that normally take the dative will occasionally take a possessive genitive. This transition is especially common where the adjective approaches the force of a noun.
- Fuit hōc quondam proprium populī Rōmānī: this was once peculiar to the Roman people. (~a peculiar trait of)
- Fuit semper amīcus Cicerōnis: he was always friendly with Cicero. (~a friend of)
- Adeō patris similis es: you’re just like your master. (~a chip off the old block)
Here’s the full list of adjectives that perform this function—
- aequālis, aequāle: of the same age (~a contemporary of)
- affīnis, affīne: related to by marriage (~kinsman of)
- aliēnus, -a, -um: belonging to another (~a stranger to)
- cōgnātus, -a, -um: fellow-born (~kinsman of)
- commūnis, commūne: common to (~kinsman of)
- cōnsanguineus, -a, -um: sharing a bloodline (~kinsman of)
- contrārius, -a, -um: opposite (~the opposite of)
- dispār: unlike (dispar suī, in philosophical diction)
- familiāris, familiāre: of close relation (~intimate of)
- fīnitimus, -a, -um: adjoining (~neighbor of)
- inimīcus, -a, -um: hostile to (~enemy of)
- necessārius, -a, -um: connected with (~component of)
- pār: equal to (~a match)
- pecūliāris, pecūliāre: personal (~peculiar trait of)
- propinquus, -a, -um: neighboring (~neighbor of)
- proprius, -a, -um: personal (~peculiar trait of)
- sacer, sacra, sacrum: holy (~holy with respect to some deity)
- similis, simile: alike to (~spitting image of)
- superstes: surviving (~survivor of)
- vīcīnus, -a, -um: neighboring (~neighbor of)
Note that this genitive construction is actually more common for proprius, -a, -um than the dative construction.
Similis with the genitive is especially common with personal pronouns (meī, tuī, suī) and within the fixed phrase vērī similis (probable).
Latin for Addicts 