additive

adj

1. Pertaining to addition; that can be, or has been, added.
2. (usually)That is distributive over addition.

   “Matrix multiplication is additive, in that M#92;vecv#43;M#92;vecw#61;M(#92;vecv#43;#92;vecw).”

3. Whose operator is identified as addition.

   “It is natural to look at a finite cyclic group as an additive group.”

4. Pertaining to chemical addition.
5. Of or pertaining to genes (or the interaction etc. of such genes) which govern the same trait and whose effects work together on the phenotype.

noun

1. A substance added to another substance or product to produce specific properties in the combined substance.

   “Oil may be used as an additive in gasoline to improve the lubrication of a small engine.”

2. A word or phrase that adds something, such as also, even, or nor.