- a musical instrument played at a pitch different from that indicated in the score.
- a musical instrument, esp a horn or clarinet, pitched in a key other than C major, but whose music is written down as if its basic scale were C major. A piece of music in the key of F intended to be played on a horn pitched in F is therefore written down a fourth lower than an ordinary part in that key and has the same key signature as a part written in C
