adverb
US/ˌɪd.i.oʊ.sɪŋˈkræt.ɪ.kəl.i/
UK/ˌɪd.i.əʊ.sɪŋˈkræt.ɪ.kəl.i/
In a way that is strange and personal, and different from how most people do it.
In context
He organizes his books idiosyncratically, by the color of the cover.
Short entry. Full notes coming.