additive (adj.)
1690s, "tending to be added," from Late Latin additivus "added, annexed," from past participle stem of Latin addere "add to, join, attach" (see addition). Alternative addititious "additive, additional" (1748) is from Latin additicius "additional."
additive (n.)
"something that is added" to a chemical solution or food product, 1945, from additive (adj.).