supplemental

1 available to supply something extra when needed the new program will provide supplemental health insurance to thousands of workers Synonyms accessorial, accessory, appurtenant, peripheral, auxiliary, supplementaryRelated Words backup, makeshift, substitute; added, additional, another, further; complementary, contributory; adjuvant, assistant, assisting, helping, supportive, tributary; secondary, subordinate, subservient, subsidiary; dispensable, excess, nonessential, superfluous, surplus, unessentialNear Antonyms basic, fundamental, primary, prime; all-important, essential, imperative, indispensable, integral, necessary, needed, needful, required, requisite, vitalAntonyms chief, main, principal

2 related to each other in such a way that one completes the other an astronomer who regards science and religion not as antithetical but as supplemental belief systems Synonyms correlative, reciprocal, complementary, supplementaryRelated Words cooperative, mutual, symbiotic; collective, combined, common, communal, conjoint, joint, shared, unitedAntonyms noncomplementary, nonreciprocal