Is the ~주 ending the agent noun ending, which is to say its the same as the English +er ending?
Hello. :D Sort of yes but not quite, I think!
nouns ending with ~주 means usually "owner"
1) 고용주 = literaly 고용(employment) + 주 (주인, master, owner ,主人 ) = employer
2) 사업주 = 사업(business) + 주 (주인, master, owner ,主人 ) = business owner
other examples would be: 3) 구단주 : 구단 (=TEAM) + 주 (주인, master,主人 ) = Team owner 4) 주주 = 주 (in this case 주 is a shortened form of 주식 which is company share) + 주 (주인, master, owner ,主人 ) = company shareholder (literally meaning "share owner")
5) 대주주: 대(big,majority 大) + 주주 (shareholder) = major shareholder
~가 might be er in English for example: 1) 사업가 = 사업 (business) + 가 (one/person doing) = business person, businessman, businesswoman, entrepreneur
2) 모험가 = 모험 (adventure) + 가 (one/person doing) = adventurer 3) 탐험가 = 탐험 (exploration) + 가 (one/person doing) = explorer 4) 화가 = painter / 만화가 =만화(cartoon, manga) + 가 (one/person doing) = cartoonist, animator 5) 작가 = professional writer / 사진작가 = 사진(photo)+작가 = photographer
Hope this helps! :D