my·e·lo·sis \ˌmīəˈlōsə̇s\noun (pluralmyelo·ses \-ōˌsēz\) Etymology: New Latin, from myel- + -osis 1. a.: the proliferation of marrow tissue to produce the changes in cell distribution typical of myelogenous leukemia b.: leukemia; especially: myelogenous leukemia 2.: the formation of a tumor of the spinal cord