What term describes a sudden strong accent of a single note or chord?

The term that describes a sudden strong accent on a single note or chord is sforzando. In musical notation, sforzando indicates that the performer should play that note or chord with an abrupt increase in volume, creating an emphasis that stands out from the surrounding musical phrases. This technique adds emotional intensity and drama to the music, making it particularly effective in certain passages where contrast is desired.

Forte refers to playing loudly, while piano indicates playing softly, neither of which conveys the abrupt emphasis required for a sudden accent. Legato, on the other hand, pertains to playing notes smoothly and connectedly, without breaks, which does not relate to the concept of accentuating a single note or chord. Therefore, sforzando is the accurate term in the context of highlighting a specific moment in the music with a strong emphasis.