subsidiary

Etymology

From Middle French subsidiaire, from Latin subsidiarius (“belonging to a reserve”).

adj

1. Auxiliary or supplemental.
   chief ruler and principal head everywhere, not suffragant and subsidiary 1603, Michel de Montaigne, translated by John Florio, Essays
   They constituted a useful subsidiary testimony of another state of existence. May 1, 1823, Samuel Taylor Coleridge, Difference between stories of dreams and ghosts […]
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. 1935, George Goodchild, chapter 5, in Death on the Centre Court
3. Of or relating to a subsidy.
   subsidiary payments to an ally
   George the Second relied on his subsidiary treaties. 1836-1853, Philip Stanhope, 5th Earl Stanhope, History of England from the Peace of Utrecht to the Peace of Versailles, 1713-1783

noun

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