A somewhat formal or literary term for a fellow worker or companion in the same profession or organization. In everyday speech, 同僚 is more common.
He is a longtime colleague, and we trust each other.
職場の僚友と協力してプロジェクトを進めた。
I worked on the project in cooperation with my workmates.
He is deeply saddened to have lost his longtime colleague.
Working in the same lab, the two of them became close colleagues.