-os·to·sis \ˌäˈstōsə̇s\noun combining form (plural-osto·sesor-ostosises \-ōˌsēz\) Etymology: New Latin, from Greek -ostōsis, from osteon bone + -ōsis -osis : ossification of a (specified) part or to a (specified) degree < hyperostosis > < ectostosis >