The Collaborative International Dictionary
Sidebone
Sidebone \Side"bone`\, n. (Far.)
A morbid growth or deposit of bony matter and at the sides of
the coronet and coffin bone of a horse.
--J. H. Walsh.
Wiktionary
sidebone
n. A morbid growth or deposit of bony matter at the sides of the coronet and coffin bone of a horse.
Wikipedia
Sidebone
Sidebone is a common condition of horses, characterized by the ossification of the collateral cartilages of the coffin bone. These are found on either side of the foot protruding above the level of the coronary band. The lateral cartilages support the hoof wall and provide an important role in the support and cushioning provided to the heel. The front feet are most commonly affected.