noun
choir member
A person who belongs to a choir or chorus group.
彼女は合唱隊員として毎週練習に参加している。
She participates in practice every week as a choir member.
合唱団 refers to the choir group itself, while 合唱隊員 refers to an individual member of that group.
Compound of 合唱 (chorus) + 隊員 (member of a group).