spacer

noun6

1. •
   An object inserted to hold a space open in a row of items, e.g. beads or printed type.

   • The vertical wall was poured in two lifts, using two pairs of steel shutters which were bolted tightly onto 9-in. long wooden spacers. — 1959
2. •
   A bushing.
3. •
   A type of add-on device used by an asthmatic person to increase the effectiveness of a metered-dose inhaler.
4. •
   A person who works or lives in space.

   • It was the futile throwing back in the face of the Spacers their most keenly felt insult: their insistence on considering the natives of Earth as disgustingly diseased. — 1954
5. •
   (slang) A forgetful person; one who spaces out.
6. •
   (historical) An instrument for reversing a telegraphic current, especially in a marine cable, to increase the speed of transmission.