Supplementary refers to something that is added to something else in order to improve it or complete it. Examples of supplementary include: ^{cambridge.org 1 2}

• Teachers often create supplementary materials for their classes.
• Some workers are eligible for supplemental unemployment benefits.
• Also included will be supplementary liability insurance, often up to $1 million, as protection against claims from any third parties.
• A supplementary budget may be needed to cover the cost of repairs.