valence

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The combining capacity of an atom or group of atoms as determined by the number of electrons it can lose, add, or share when it reacts with other atoms or groups.
• noun An integer used to represent this capacity, which may be given as positive or negative depending on whether electrons are lost or gained, respectively.
• noun The number of binding sites of a molecule, such as an antibody or antigen.
• noun The number of different antigens contained in a vaccine, corresponding to the number of pathogens that it is active against.
• noun Psychology The degree of attraction or aversion that an individual feels toward a specific object or event.
• noun Linguistics The number and type of arguments that a lexical item, especially a verb, can combine with to make a syntactically well-formed sentence, often along with a description of the categories of those constituents. Intransitive verbs (appear, arrive) have a valence of one—the subject; some transitive verbs (paint, touch), two—the subject and direct object; other transitive verbs (ask, give), three—the subject, direct object, and indirect object.
• noun The capacity of something to unite, react, or interact with something else.

from The Century Dictionary.

• noun In chem., the relative saturating or combining capacity of an atom compared with the standard hydrogen atom; the quality or force which determines the number of atoms with which any single atom will chemically unite.
• noun In biology: Form value; morphological value or equivalency. See morphic.
• noun In zoology, taxonomic value or equivalency; classificatory grade or rank of a zoölogical group.
• See valance.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) The degree of combining power of an atom (or radical) as shown by the number of atoms of hydrogen (or of other monads, as chlorine, sodium, etc.) with which it will combine, or for which it can be substituted, or with which it can be compared; thus, an atom of hydrogen is a monad, and has a valence of one; the atoms of oxygen, nitrogen, and carbon are respectively dyads, triads, and tetrads, and have a valence respectively of two, three, and four.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Alternative spelling of valance.
• noun chemistry, obsolete An extract; a preparation.
• noun chemistry The combining capacity of an atom, radical or functional group determined by the number of electrons that it will lose, gain, or share when it combines with other atoms etc
• noun chemistry The number of binding sites of a molecule, such as an antibody or antigen
• noun linguistics The number of arguments that a verb can have, including the subject of the verb in the counting, ranging from zero (for the likes of "It rains") to three (for the likes of "He gives her a flower").
• noun psychology A one-dimensional value assigned to an object, situation, or state, that can usually be positive or negative
• noun sociology value

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (biology) a relative capacity to unite or react or interact as with antigens or a biological substrate
• noun (chemistry) a property of atoms or radicals; their combining power given in terms of the number of hydrogen atoms (or the equivalent)