noun

a person who is very knowledgeable about or skilful in a particular area.

an expert in healthcare

specialist,authority,pundit,oracle,resource person,adept,maestro,virtuoso,master,past master,professional,genius,wizard,connoisseur,aficionado,one of the cognoscenti,cognoscente,doyen,savant,ace,buff,ninja,pro,whizz,hotshot,old hand,alpha geek,dab hand,maven,crackerjack,proficient

adjective

having or involving a great deal of knowledge or skill in a particular area.

he had received expert academic advice

skilful,skilled,adept,accomplished,talented,fine,master,masterly,brilliant,virtuoso,bravura,magnificent,marvellous,wonderful,outstanding,great,exceptional,superlative,formidable,excellent,dazzling,first-class,first-rate,elite,superb,proficient,good,able,apt,capable,competent,clever,experienced,practised,qualified,knowledgeable,well versed,specialist,professional,deft,dexterous,adroit,au fait,wizard,ace,stellar,class,crack,top-notch,out of this world,mean,A1,demon,genius,shit hot