(crystallography, mineralogy) The set of all symmetry operations that can be applied to a given crystal without changing it.

plural of space hopper

The period from the about the time of the launch of Sputnik in 1957 to the present day, during which people ventured into space. / (attributive) Redolent of the space age; appearing futuristic or modern.

That part of an electron tube in which electrons interact with a modulated field

That part of an optical system where real or virtual images are formed

A broad step between flights of a staircase. / (mathematics) Either of the two parts of three-dimensional space divided by a plane.

(mathematics) Any topological space which cannot be written as the disjoint union of two or more nonempty open spaces.

(mathematics) Any Riemann space in which the metric tensors are constants throughout

To type (or format) text without leaving a blank line between each line of text. / To type (or format) text with only one space between consecutive sentences.

Sufficient space or a span of time in which to recover one's breath. / A rest, pause, or respite. / Enough distance so that one can feel unfettered.