Bourdon (bell)
The bourdon is the heaviest of the bells that belong to a musical instrument, especially a chime or a carillon, and produces its lowest tone. The name derives from the French word for bumblebee.
Although carillons are by definition chromatic, the next bell up from the bourdon is traditionally a whole tone higher in pitch, leaving a semitone out of the instrument. Bells separated from the next higher note by more than two semitones (one whole tone) are called sub-bourdons.