additive
ad-di-tive
adjective
Relating to or characterised by addition; able to be added or combined.
"The combined effects were purely additive."
noun
A substance added to something to improve, preserve, or modify it.
"Many processed foods contain artificial additives."
Thesaurus
Synonyms: linear, bilinear, accumulative, summational, cumulative, supplemental, complemental, complementary, incremental, extra, intercalary, supplementary
Antonyms: nonlinear, subtractive