дополни́тельный — meaning in English

dopolnitelnyy

English meaning

accessory noun An additional item that complements or completes something, especially an outfit.
additional adjective Extra; added on top of what already exists.
adjunct noun Something added or attached to a main thing, in a lesser role.
adventitious adj Coming from outside, rather than being a natural part of something.
ancillary adjective Providing support to something more important, without being an essential part of it.
auxiliary adjective Providing extra help or support to something else, rather than being the main part.
extra adj More than what is usual, expected, or included as standard; additional.
subsidiary noun A company that is owned or controlled by a larger parent company.
supplemental adj Serving to supplement something; additional.
supplementary adj Added to provide something extra that was needed.

дополни́тельный is used for these senses in English:

accessory Having a secondary, supplementary or subordinate function by accompanying as a subordinate; aiding in a secondary way; being additional; contributing or being contributory. [from 1550s]
additional Supplemental or added to something.
adjunct Connected in a subordinate function.
ancillary Subordinate; secondary; auxiliary.
extra (not comparable) Beyond what is due, usual, expected, or necessary; extraneous; additional; supernumerary.
subsidiary Auxiliary or supplemental.
supplementary Additional; added to supply what is wanted.
top-up That serves as an addition

noun An additional item that complements or completes something, especially an outfit.
noun A person who helps someone commit a crime without directly carrying it out.
adj Supplementary or secondary rather than essential.