subsidiary

adj

1. Auxiliary or supplemental.

   “chief ruler and principal head everywhere, not suffragant and subsidiary”

   “They constituted a useful subsidiary testimony of another state of existence.”

2. Secondary or subordinate.

   “a subsidiary stream”

   “By one o'clock the place was choc-a-bloc. […] The restaurant was packed, and the promenade between the two main courts and the subsidiary courts was thronged with healthy-looking youngish people, drawn to the Mecca of tennis from all parts of the country.”

3. Of or relating to a subsidy.

   “subsidiary payments to an ally”

   “George the Second relied on his subsidiary treaties.”

noun

1. A company owned by a parent company or a holding company, also called daughter company or sister company.
2. A subordinate theme.
3. One who aids or supplies; an assistant.