noun

• (countable, chemistry) Alternative form of valence (“the combining capacity of an atom, functional group, or radical determined by the number of atoms of hydrogen with which it will unite, or the number of electrons that it will gain, lose, or share when it combines with other atoms, etc.”).
• (countable, chemistry) Alternative form of valence (“the combining capacity of an atom, functional group, or radical determined by the number of atoms of hydrogen with which it will unite, or the number of electrons that it will gain, lose, or share when it combines with other atoms, etc.”).
  "vaccine valency"
• (countable, graph theory) The number of edges connected to a vertex in a graph.
• (countable, linguistics) Alternative form of valence (“the number of arguments that a verb can have, including its subject, ranging from zero to three or, less commonly, four”).