"to cause to work too hard," 1520s, from over- + work (v.). The figurative sense of "to work into a state of excitement and confusion" is by 1640s. Old English oferwyrcan meant "to work all over," i.e. "to decorate the whole surface of." Related: Overworked; overworking.
"work beyond a person's strength, excessive labor," 1819; see overwork (v.). Middle English ofer-werc, Old English ofer-geweorc (West Saxon) meant "a superstructure, a work raised over something," hence "sarcophagus, tomb."