The Collaborative International Dictionary
Malacosteon
Malacosteon \Mal`a*cos"te*on\, n. [NL., Gr. fr. malako`s soft + 'oste`on bone.] (Med.) A peculiar disease of the bones, in consequence of which they become softened and capable of being bent without breaking.
Wiktionary
malacosteon
n. (context pathology English) morbid softness of the bones; osteomalacia.