[n] something added to enhance food or gasoline or paint or medicine [adj] characterized or produced by addition; "an additive process" [adj] (mathematics) directly proportional
accumulative, addable, addible, bilinear, cumulative, linear, summational, summative
nonlinear, subtractive
accession, accessory, accompaniment, accumulative, addenda, addendum, additament, addition, additional, additory, additum, adjunct, adjuvant, annex, annexation, appanage, appendage, appendant, appurtenance, appurtenant, attachment, augment, augmentation,