British Imperial System vs British system

British Imperial System and British system both are nouns.

Word	Noun	Adjective	Verb	Adverb
British Imperial System	Yes	No	No	No
British system	Yes	No	No	No

As nouns, British Imperial System and British system are synonyms defined as:

British Imperial System and British system: a system of weights and measures based on the foot and pound and second and pint

Other synonyms of British Imperial System include English system.

British Imperial System (noun)	British system (noun)
a system of weights and measures based on the foot and pound and second and pint	a system of weights and measures based on the foot and pound and second and pint