supplement B2

/ˈsʌp.lə.mənt/ Something added to make up for what is missing or to improve something.

supplemental C2+

/ˌsʌpləˈmɛntəl/ added to complete or enhance something; additional

supplementary C2+

/ˌsʌpləˈmɛntɛri/ completing or enhancing something by providing an addition