Pronunciation: (u-nēl'),[key] —v.t. 1. to heat (glass, earthenware, metals, etc.) to remove or prevent internal stress.
2. to free from internal stress by heating and gradually cooling.
3. to toughen or temper.
4. Biochem.to recombine (nucleic acid strands) at low temperature after separating by heat.
5. to fuse colors onto (a vitreous or metallic surface) by heating.