10 letters · 15 points in Scrabble
noun a musical notation that makes a note sharp or flat or natural although that is not part of the key signature
adjective happening by chance or unexpectedly or unintentionally
originFrom Middle English accidental, from Anglo-Norman accidentel, Middle French accidentel, accidental, and their source, Late Latin accidēntālis; corresponding to accident + -al.
Etymology from Wiktionary, CC BY-SA 3.0