Pull the Plug

The literal image could come from either of two everyday sources, and etymologists genuinely can't say which one gave rise to the phrase first. Plugs and stoppers on tubs, basins, and even early flushing cisterns are centuries old, so "pulling the plug" to drain water is at least an 18th-century practice. Electrical plugs offer an equally plausible source, since cutting power to a machine by unplugging it produces the same instant, decisive stop. The figurative sense, meaning to end a project or withdraw support, is documented from around the 1940s, with the specific medical sense, taking someone off life support, following in the 1960s.