| Subject | English | Basque |
| comp., MS | addition operator | batuketaren eragile (The + character, used to indicate addition or a positive number) |
| environ. | addition polymer A polymer formed by the chain addition of unsaturated monomer molecules, such as olefins, with one another without the formation of a by-product, as water; examples are polyethylene, polypropylene and polystyrene | adizio-polimero |
| environ. | chemical addition Chemical reaction in which one or more of the double bonds or triple bonds in an unsaturated compound is converted to a single bond by the addition of other atoms or groups | adizio kimiko |