combining weight

GNU Webster's 1913

1. v. (Chem.) that proportional weight, usually referred to hydrogen as a standard, and for each element fixed and exact, by which an element unites with another to form a distinct compound. The combining weights either are identical with, or are multiples or submultiples of, the atomic weight. See Atomic weight, under Atomic, a.

WordNet 3.0

1. n. the atomic weight of an element that has the same combining capacity as a given weight of another element; the standard is 8 for oxygen