early 15c., procusie, proccy, prokecye, "agency of one who acts instead of another, office or authority of a substitute; letter of power of attorney," contraction of Anglo-French procuracie (c. 1300), from Medieval Latin procuratia "administration," from Latin procuratio "a caring for, management," from procurare "manage" (see procure). Also compare proctor (n.).
Meaning "person who is deputed to represent or act for another" is from 1610s. Of things, "that which takes the place of something else," 1630s. Meaning "vote sent by a deputy" is from 1650s in a Rhode Island context. Proxy war, one started or stoked by, but not directly involving, a major power is by 1955.