Noun, pl. Diaphyses
1. The main or midsection (shaft) of a long bone. It is made up of cortical bone and usually contains bone marrow and adipose tissue (fat). (wikipedia.org)
2. The central shaft of any long bone. (wiktionary.org)
3. The body of a long bone between the growing regions near the ends. (wordnetweb.princeton.edu)
Word origin: Greek dia = apart, and physis = growth.