supplemental
adj.adj. added to something else to make it better or more complete. You use this to describe extra things that help you finish a task or understand a topic.
adj. added to something else in order to complete or enhance it. Often refers to additional materials, income, or information that supports a primary source.
The teacher gave us supplemental reading for the exam.
He took a part-time job in the evenings to provide supplemental income for his growing family.
The report includes supplemental data in the appendices to support the primary findings presented in the executive summary.
From supplement + -al.
Typically used attributively before a noun. Often interchangeable with 'supplementary', though 'supplemental' is more common in American English legal and academic contexts.