空: the sky, empty air

空転: idling

空転: to idle

区域: area, district

teacher

classroom

tutor; coach

missionary

(education) instruction that takes place outside of a classroom (field trip, etc.) / (education) class that takes place in its own specialized room instead of homeroom (such as music or cooking)

(mathematical analysis) Banach space - a normed vector space which is complete, in the sense that Cauchy sequences converge