1relating to a system, especially as opposed to a particular part:the disease is localized rather than systemic
2 Physiology denoting the part of the circulatory system concerned with the transport of oxygen to and carbon dioxide from the body in general, especially as distinct from the pulmonary part concerned with the transport of oxygen from and carbon dioxide to the lungs.
3(of an insecticide, fungicide, or similar substance) entering the plant via the roots or shoots and passing through the tissues.
early 19th century: formed irregularly from system+ -ic
systemic in other Oxford dictionaries
Definition of systemic in the US English dictionary