fixative

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

• noun Something that fixes, protects, or preserves, especially.
• noun A liquid preservative applied to artwork, such as watercolor paintings or charcoal drawings.
• noun A solution used to preserve and harden fresh tissue for microscopic examination.
• noun A liquid mixed with perfume to prevent rapid evaporation.

from The Century Dictionary.

• Serving to fix, or make fixed or stable: as, a fixative substance or process.
• noun Anything which serves to render fixed or stable, as a mordant with reference to colors; specifically, a weak solution of shellac in alcohol applied to charcoal and crayon drawings with an atomizer to fix them and prevent them from being rubbed.
• noun In perfumery, a substance used to detain from too speedy evaporation a highly volatile ingredient of agreeable odor. The substance so used may itself be inodorous or may contribute to the blended odor of the mixed perfume.
• noun Same as amboceptor.

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

• noun That which serves to set or fix colors or drawings, as a mordant.

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

• noun A substance that fixes, protects, or preserves.
• adjective Serving to fix or bind.

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

• noun a compound (such as ethanol or formaldehyde) that fixes tissues and cells for microscopic study
• noun a varnish dissolved in alcohol and sprayed over pictures to prevent smudging