The Collaborative International Dictionary of English v.0.48:

Additive \Ad"di*tive\, a. [L. additivus.] (Math.)
   Proper to be added; positive; -- opposed to subtractive.
   [1913 Webster]

WordNet (r) 3.0 (2006):

additive
    adj 1: designating or involving an equation whose terms are of
           the first degree [syn: linear, additive] [ant:
           nonlinear]
    2: characterized or produced by addition; "an additive process"
       [ant: subtractive]
    n 1: something added to enhance food or gasoline or paint or
         medicine

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "additive":
   accession, accessory, accompaniment, accumulative, addenda,
   addendum, additament, addition, additional, additory, additum,
   adjunct, adjuvant, annex, annexation, appanage, appendage,
   appendant, appurtenance, appurtenant, attachment, augment,
   augmentation, chain, coda, complement, component, concomitant,
   constituent, continuation, corollary, cumulative, elemental,
   extension, extrapolation, fixture, increase, increment, offshoot,
   pendant, reinforcement, side effect, side issue, summational,
   summative, supplement, tailpiece, undergirding



The Free On-line Dictionary of Computing (30 December 2018):

additive

    A function f : X -> Y is additive if

    for all Z <= X
    f (lub Z)  =  lub  f z : z in Z 

   (f "preserves lubs").  All additive functions defined over
   cpos are continuous.

   ("<=" is written in LaTeX as \subseteq, "lub" as \sqcup ).

   (1995-02-03)