expander

/IH0 K S P AE1 N D ER0/
noun
  1. 1

    One who or that which expands.

  2. 2

    (graphical user interface) A control that expands to show more options or commands, keeping them hidden until needed.

  3. 3

    (dentistry) A device used to widen the upper jaw so that the bottom and upper teeth will fit together better; a palatal expander.

  4. 4

    (graph theory) A kind of sparse graph with strong connectivity properties.