Etymology From Middle French subsidiaire, from Latin subsidiarius (“belonging to a reserve”).
1
Auxiliary or supplemental.
chief ruler and principal head everywhere, not suffragant and subsidiary1603, 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