megakaryocyte(n = noun.body) - a large bone marrow cell; regarded as the source of blood platelets;
is a kind of bone cell
Derived form adjective megakaryocytic₁

   A large bone marrow cell not usually found in the circulating blood; it is regarded as the precursors of blood platelets; it is up to 100 megacaryocyte, megalokaryocyte, and thromboblast. [WordNet 1.5]