planetarium /ˌplænəˈterijəm/ noun plural planetariums or planetaria /-ijə/ /ˌplænəˈterijə/ plural planetariums or planetaria /-ijə/ /ˌplænəˈterijə/ Learner's definition of PLANETARIUM
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: a building or room in which images of stars, planets, etc., are shown on a high, curved ceiling天文馆;天象馆