As mentioned in my comment above, the word the asker was looking for is declare. See the relevant Wikipedia article on the concept of "declaration" in programming.
A quote from the above, with some minor changes in square brackets:
In computer programming, a declaration is a language construct specifying identifier properties: it declares a word's (identifier's) meaning. Declarations are most commonly used for functions, variables, constants, and classes, but can also be used for other entities such as enumerations and type definitions. [...]
A declaration is used to announce the existence of the entity to the compiler [or interpreter]; this is important in those strongly typed languages that require functions, variables, and constants, and their types to be specified with [declarations.]