valency
The capacity of something to combine with other things, as for example the capability of a vaccine as measured by the number of pathogen that it can counteract.
Other meanings
The number of edges connected to a vertex in a graph.
Importance, significance.
Word history
From Latin "valentia" (bodily strength; health; vigour).
Where this comes from
This definition is adapted from “valency” on Wiktionary, by its contributors, published under CC BY-SA 4.0. This page is published under the same licence.