If a company belongs to another company, then the owned company is a subsidiary. When a large company bought your small business, you became a subsidiary. It still hurts to call them the parent company, since you publish novels and they make toilet paper.
The adjective form of subsidiary describes something that is of secondary importance or that functions in a supporting capacity. In addition to running the band program, you're a member of several subsidiary committees like the fund raising committee and the hospitality committee. Traffic on the road was light when you drove outside the city, but as more subsidiary roads joined with the main one, traffic quickly became congested.