supplement
Definitions
Something added to complete a thing, make up for a deficiency, or extend or strengthen the whole.
A substance taken to improve one's diet or health, such as a vitamin or mineral.
To add an extra element or amount to something.
Examples
You should take a vitamin supplement to ensure you get enough nutrients.
Many students take an online course to supplement their classroom learning.
He works a part-time job to supplement his primary income.