spacer

noun

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.”

2. 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.”

   “"How do I know I can trust you?" asked BKR. Grakker hesitated. "Spacer's oath," he said at last.”

   “Shepard: What are you running for? Charles Saracino: I'm seeking one of the five spacer seats in Parliament. They have certain baroque conditions for a citizen to be able to vote for them. Charles Saracino: You have to spend more than six months a year in space. But you can't have stayed in any one settled system for more than a month.”

   “He was thankful that he still had his suit on when the ship had a catastrophic decompression, a spacer's worst nightmare.”

3. A bushing.
4. (slang)A forgetful person; one who spaces out.
5. A type of add-on device used by an asthmatic person to increase the effectiveness of a metered-dose inhaler.
6. (historical)An instrument for reversing a telegraphic current, especially in a marine cable, to increase the speed of transmission.