(typography, in fonts whose ideographs are of uniform width) A space of non-variable width: ⊣　⊢ equal to the width of an ideograph, used in Chinese, Japanese, Korean, and other languages that use Siniform ideographs.

(obsolete) The volume of the conducting airways of the lung. This definition became inadequate once the alveolar dead space was described.

(anatomy) That volume of conducting airways of the lung, as measured by a cast of the airways.

(physiology) The volume of air in the alveoli of the lung which does not partake in the exchange of gas.

plural of space opera

(art) The space around and between the subjects of an image.

The informal competition between the United States and the Soviet Union to launch unmanned satellites, send people into space and land them on the Moon.

vector space

Alternative spelling of spacefaring

The quotient of a Hilbert space by an equivalence relation which considers a pair of vectors equivalent iff they differ only by a factor which is a complex number.