synostosis 

Union of two or more separate bones to form a single bone.
(Examples)
• craniosynostosis: Cranial bones.
• radioulnar synostosis: The radius and ulna bones.
• tarsal coalition: A failure to separately form all seven bones of the tarsus resulting in an amalgamation of two bones.
• syndactyly: Neighboring digits.
(Comparison)
• synostosis: Union of multiple bones to form a single bone.
• ankylosis: Synostosis occurring within joints. The abnormal immobility can be caused by a disease, injury, or surgical procedure.
• dysostosis: A genetic disorders in a single or group of bones, in particular affecting ossification.
• osteochondroma: A noncancerous overgrowth of cartilage and bone that happens at the end of the bone near the epiphyseal plate. It most often occurs between ages 10 and 30.
• osteochondrodysplasia (skeletal dysplasias): A group of hereditary disorders of connective tissue, bone, or cartilage that cause the skeleton to develop abnormally.
(Comparison about the epiphyseal plate)
Fusion of the epiphyseal plate (synostosis) normally occurs to form the epiphyseal line in puberty.
Multiple epiphyseal dysplasia (Fairbank's disease) is a genetic disorder, which the process in the epiphyseal plate is defective.