license plate vs numberplate

license plate and numberplate both are nouns.

Word	Noun	Adjective	Verb	Adverb
license plate	Yes	No	No	No
numberplate	Yes	No	No	No

As nouns, license plate and numberplate are synonyms defined as:

license plate and numberplate: a plate mounted on the front and back of car and bearing the car's registration number

license plate (noun)	numberplate (noun)
a plate mounted on the front and back of car and bearing the car's registration number	a plate mounted on the front and back of car and bearing the car's registration number