议员(yì yuán) - member of parliament, councillor, legislator in Mandarin

议员 (yì yuán) is anyone who sits in an elected assembly and votes: a member of parliament, a senator, a congressman, a city councillor. Chinese does not split these the way English does, so the specific body is named in front when it matters, as in 国会议员 or 市议员.

You will meet it most in news reporting about other countries, which is where the word does most of its work. The verb that goes with it is 当, to serve as: 他当了议员 means he became an MP, not that he owned one.

The trap is reaching for 议员 to translate "politician" in general. That is 政治家 or, more coolly, 政客. 议员 is a job description tied to a seat in an assembly, so a prime minister described only as 议员 sounds oddly demoted. Note also that 员 marks a person by role, and it recurs everywhere: 服务员 waiter, 演员 actor, 会员 member.