/plan'i tair"ee euhm/ , n. , pl. planetariums, planetaria /-tair"ee euh/ .
1. an apparatus or model representing the planetary system.
2. a device that produces a representation of the heavens by the use of a number of moving projectors.
3. the building or room in which such a device is housed.
[ 1765-75; planetarius PLANETARY; cf. -ARIUM ]