1. An inherent likeness or relationship.

2. A special attraction for a specific element, organ or structure.

3. <chemistry> The force that binds atoms in molecules, the tendency of substances to combine by chemical reaction.

4. The strength of noncovalent chemical binding between two substances as measured by the dissociation constant of the complex.

5. <immunology> A thermodynamic expression of the strength of interaction between a single antigen binding site and a single antigenic determinant (and thus of the stereochemical compatibility between them), most accurately applied to interactions among simple, uniform antigenic determinants such as haptens. Expressed as the association constant (K litres mole 1), which, owing to the heterogeneity of affinities in a population of antibody molecules of a given specificity, actually represents an average value (mean intrinsic association constant).

6. <chemistry> The reciprocal of the dissociation constant.

Origin: L. Affinitas = relationship

(06 Oct 1997)