A numerative is a °bound °morph that is one of several which occur in complementary distribution next to an °adnominal °cardinal numeral (and possibly next to other adnominal modifiers), but not next to a °predicating form, and whose choice is determined by the class of the numerated °noun rather than contributing a meaning of its own.
The definition is from Haspelmath (2025). A more common term is "numeral classifier", but this term is sometimes used more broadly (not only for "sortal numeral classifiers", but also for "mensural numeral classifiers"), and it suggests that a numeral classifier is a kind of "classifier". This latter term is not well-defined, so the term "numerative" seems more appropriate.