space-time continuum vs space-time

space-time continuum and space-time both are nouns.

Word	Noun	Adjective	Verb	Adverb
space-time continuum	Yes	No	No	No
space-time	Yes	No	No	No

As nouns, space-time continuum and space-time are synonyms defined as:

space-time continuum and space-time: the four-dimensional coordinate system (3 dimensions of space and 1 of time) in which physical events are located

space-time continuum (noun)	space-time (noun)
the four-dimensional coordinate system (3 dimensions of space and 1 of time) in which physical events are located	the four-dimensional coordinate system (3 dimensions of space and 1 of time) in which physical events are located