adjuvant
US /ˈædʒ.ə.vənt/
UK /ˈædʒ.ə.vənt/

1.
a substance which enhances the body's immune response to an antigen.
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The vaccine contains an adjuvant to boost its effectiveness.
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Certain chemicals can act as adjuvants in agricultural sprays.
1.
assisting or enhancing the action of a primary medical treatment, drug, or other agent.
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Adjuvant therapy is often used after surgery to prevent cancer recurrence.
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The drug has an adjuvant effect when combined with other medications.