Noun

1. subordinate, subsidiary, underling, foot soldier, assistant, helper, help, supporter

usage: an assistant subject to the authority or control of another

2. subsidiary company, subsidiary, company

usage: a company that is completely controlled by another company

Adjective

1. auxiliary, subsidiary, supplemental, supplementary, secondary (vs. primary)

usage: functioning in a supporting capacity; "the main library and its auxiliary branches"

See also: subsidiary (Dictionary)