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

(mathematics, geometry) Euclidian space - a space where the prinicples of Euclidean geometry apply.

(electronics) vacuum tube

(idiomatic) waste time on the way, loiter on the way

something extremely uncommon

living space

airbase (military airport)

outer space

(engineering) aerospace engineering

kick-off (opening kick of a game) / opening stage of something