The Vocalibrate dictionary

idiosyncratic

/ˌɪdioʊsɪŋˈkrætɪk/adjective

peculiar to one person; unlike anyone else's

Her idiosyncratic filing system made sense to her but baffled everyone else.

Near in meaning: peculiarquirkydistinctiveindividual
In the family: idiosyncrasyidiosyncratically

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