A person who supports communist ideology or is a member of a communist party; denotes a political stance.
若い頃、彼は共産主義者として活動していた。
In his youth, he was active as a communist.
討論会で共産主義者と資本主義者が議論した。
At the debate, a communist and a capitalist argued their points.
彼女は共産主義者だと噂されたが、本人は否定した。
She was rumored to be a communist, but she denied it.