noun

• (linguistics) A word whose meaning changes depending on the situation, as by deixis.
  "The cigarette is analogous to what linguists call a shifter, like the word I ; this device for expressing the irreducible particularity of my innermost self is universally available to every speaker and is thus the least particular thing in the world. The smoker manipulates the cigarette, like the word I, to tell stories to him/herself about him/herself — or to an other."
• (dated) Someone who plays tricks; a trickster.
  "'Twas ſuch a ſhifter, that if truth were known, / Death was half glad when he had got him down;"
• (nautical) An assistant to the ship's cook in washing, soaking, and shifting the salt provisions.
• (engineering) A control device (usually a lever or button) for shifting gears in a gearbox, or an arrangement for shifting a belt sidewise from one pulley to another.