How to Say "supplementary" in Spanish
The Spanish word for “supplementary” is “extraordinaria” — B2 level.
English → SpanishB2
adjectiveB2formal
additional or extra

Examples
El director convocó una reunión extraordinaria para discutir la crisis.
The director called a special meeting to discuss the crisis.
La empresa pagará una bonificación extraordinaria este mes.
The company will pay a supplementary bonus this month.
Necesitamos una fuente de financiación extraordinaria.
We need an extraordinary source of funding.
Formal Context
In this sense, 'extraordinaria' refers to things that happen outside the usual schedule, such as 'elecciones extraordinarias' (snap elections).
Related Translations
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