supplemental
UK: ˌsʌplɪˈmɛnt(ə)l | US: ˌsʌpləˈmɛnt(ə)l
adj. providing additional support or reinforcement
adj. serving as a supplement; extra or non-essential
The word "supplemental" derives from Latin supplementum (a filling up, addition), formed from supplere ("to fill up," from sub- "under" + plere "to fill"). The suffix -al (from Latin -alis) converts nouns into adjectives, giving "supplemental" its meaning of "acting as an addition." The term reflects the logic of completing or enhancing something by adding to it.
The teacher provided supplemental materials for advanced learners.
A supplemental income helped her cover unexpected expenses.
The report includes a supplemental appendix with detailed data.
Vitamin D is often taken as a supplemental nutrient.
The contract had a supplemental clause added later.