Fixative: A medium such as a solution or spray that preserves specimens of tissues or cells. Most biopsies and specimens removed at surgery are fixed in a solution such as formalin (dilute formaldehyde) before further processing takes place. Other common ingredients used in fixatives are alcohol, mercuric chloride, potassium dichromate and sodium sulfate.

"Fixative" is derived from the Latin "figere" (to fix, fasten, make stable). Related English words include "fixture" (that which remains stable and in place) and "fixity" (state of being stable, steady, permanent).