(in nouns 构成名词 a person connected with something or doing an activity 与…有关的人 auctioneer 拍卖商 mountaineer 登山运动员
(in verbs 构成动词 to be connected with something or doing an activity 与…有关 profiteer 牟取暴利 commandeer 强占
Word Originfrom French -ier, from Latin -arius; verbs are often back-formations (e.g. electioneer from electioneering).