proficient vs expert

proficient is not a noun while expert is a noun.

Word	Noun	Adjective	Verb	Adverb
proficient	No	Yes	No	No
expert	Yes	Yes	No	No

As adjectives, proficient and expert are synonyms defined as:

proficient and expert: having or showing knowledge and skill and aptitude

Other synonyms of proficient include adept, good, practiced, skilful, skillful.

proficient (noun)	expert (noun)
	a person with special knowledge or ability who performs skillfully

proficient (adjective)	expert (adjective)
of or relating to technique or proficiency in a practical skill	having or showing knowledge and skill and aptitude
having or showing knowledge and skill and aptitude	of or relating to or requiring special knowledge to be understood