additive

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."

(grammar) A word or phrase that adds something, such as also, even, or nor.

Pertaining to addition; that can be, or has been, added.

(of a function, etc.) That is distributive over addition.

"Matrix multiplication is additive, in that M\vec v+M\vec w=M(\vec v+\vec w)."

(of a group, semigroup, etc.) Whose operator is identified as addition.

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