idiosyncrasy vs. idiosyncracy

The ending “-acy” is a suffix that indicates nouns of quality, state, or office, usually attaching to existing nouns or adjectives that end in “-ate,” as in accuracy (from the adjective accurate), candidacy (from the noun candidate), literacy (from the adjective literate), or piracy (from the noun pirate).

This common spelling pattern very often leads to the misspelling idiosyncracy; however, the correct spelling is idiosyncrasy. Unfortunately, there is no easy way to remember this; it is just an unusual spelling that we have to memorize.