adjective. ['ˌæksəˈdɛntəl, ˌæksəˈdɛnəl'] happening by chance or unexpectedly or unintentionally.
noun. ['ˌæksəˈdɛntəl, ˌæksəˈdɛnəl'] a musical notation that makes a note sharp or flat or natural although that is not part of the key signature.