Originally: resulting in or characterized by weakness or debility; specifically designating fevers, especially typhus and typhoid, which have a marked debilitating effect (now rare). In later use: specifically exhibiting, characterized by, or resulting from reduced or absent muscular contraction.
2Designating bone or bone disorders in which new bone formation is greatly diminished or absent.
Early 19th century; earliest use found in The Monthly Review. From a- + dynamic.