(1) The condition of being firmly attached or set. (2) In histology, the rapid killing of tissue elements and their preservation and hardening to retain as nearly as possible the same relationship they had in the living body. SYN: fixing. (3) In chemistry, the conversion of a gas into solid or liquid form by chemical reactions, with or without the help of living tissue. (4) In psychoanalysis, the quality of being firmly attached to a particular person, object, or period in one's development. (5) In physiologic optics, the coordinated positioning and accommodation of both eyes that result in bringing or maintaining a sharp image of a stationary or moving object on the fovea of each eye. [L. figo, pp. fixus, to fix, fasten]