Kinetics: Kinetics (with an "s" at the end) refers to the rate of change in a biochemical (or other) reaction, the study of reaction rates. Kinetics is a noun. It is distinct from "kinetic" (an adjective) meaning with movement. The opposite of kinetic is akinetic meaning without movement. In neurology, kinetic and akinetic serve to denote the presence or absence of movement. Kinetic comes from the Greek word "kinesis" for motion. The term "akinetic" is put together from the prefix "a-" meaning "without" + "kinesis" = without motion. Kinesis is verbatim from the Greek "kinesis."