[hahr-dn-er] 
| 1. | a person or thing that hardens. |
| 2. | a substance mixed with paint or other protective covering to make the finish harder or more durable. |
| 3. | Photography. a chemical used to raise the melting point of an emulsion. |
| hard·en·er (här'dn-ər) n. One that hardens, especially a substance added to varnish or paint to give it a harder surface or finish. |
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