"one of several kinds of apparatus for forcing liquid or air," early 15c., pumpe, which is probably from Middle Dutch pompe "water conduit, pipe," or Middle Low German pumpe "pump" (Modern German Pumpe), both from some North Sea sailors' word, possibly imitative of the sound of the plunger in the water.
Earliest English uses are in reference to a device to raise and expel bilge water from ships. Late Old French pompe probably is from Germanic. Pumps themselves are very ancient, which makes the late appearance of the Germanic word odd. From 1670s as "an act of pumping." Pump-action in reference to a type of repeating firearm is attested in advertisements for them from 1912.
1550s, "kind of low shoe or slipper without fasteners, for wearing indoors," a word of unknown origin, perhaps echoic of the sound made when walking in them, or perhaps from Dutch pampoesje, from Javanese pampoes, which is said to be of Arabic origin. Klein's sources propose a connection with pomp (n.). Related: pumps.
The word soon was applied to a shoe of the same character, with a very low heel, convenient in situations where freedom of movement was required, thus favored by "dancers, couriers, acrobats, duellists, etc." [OED]. The 19c. phrase keep your toes in your pump was dialectal for "stay calm, keep quiet, don't get excited."
c. 1500, "work with a pump, raise water or other liquid with a pump," from pump (n.1). The metaphoric extension "subject (a person) to a process resembling pumping" (to elicit information, money, etc.) is from 1630s. Transitive sense of "free from water or other fluid by means of a pump or pumps" is by 1640s. The meaning "to work with action like that of a pump-handle" is by 1803. To pump iron "lift weights for fitness" is by 1972.
Related: Pumped; pumping. Pumped up "raised artificially by a method likened to pumping" is by 1792; the sense of "excited, ready for action" is modern. Grose, in "Dictionary of the Vulgar Tongue" (1788) has "To pump ship; to make water, and sometimes to vomit."