improvisation vs temporary expedient

improvisation and temporary expedient both are nouns.

Word	Noun	Adjective	Verb	Adverb
improvisation	Yes	No	No	No
temporary expedient	Yes	No	No	No

As nouns, improvisation and temporary expedient are synonyms defined as:

improvisation (noun)	temporary expedient (noun)
an unplanned expedient	an unplanned expedient
a performance given extempore without planning or preparation
a creation spoken or written or composed extemporaneously (without prior preparation)