There are multiple definitions - click on the translation that matches your context.

tillegg

substantiv

full

supplement

noun

Definitions of supplement

a sum of money that you have to pay for an extra service or thing

There's a supplement of $50 for each additional person.

something that is added to a book, report or other document etc to complete it or to improve it

Did you get the supplement to the guidelines I sent this morning?

something that is added to something else to complete it or to improve it

The case has opened the debate about drug testing in sport and the use of supplements.