from The American Heritage® Dictionary of the English Language, 4th Edition
- n. One that hardens, especially a substance added to varnish or paint to give it a harder surface or finish.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. One who, or that which, hardens.
- n. A chemical substance added to something in order to harden it; used especially with paints, varnishes and resins.
from the GNU version of the Collaborative International Dictionary of English
- n. One who, or that which, hardens; specif., one who tempers tools.
from The Century Dictionary and Cyclopedia
- n. One who or that which makes hard or more firm and compact; specifically, one who brings cutting instruments or tools up to the required temper; a temperer.
- n. In photography, a chemical, such as alum, which is added to the fixing-bath in the making of gelatin negatives. It prevents the dissolving of the film in warm weather.
harden + -er (Wiktionary)