1. To add a poisonous or unpleasant substance to ethanol to make it unsuitable for human consumption (see methylated spirits).
2. To produce a structural change in a protein or nucleic acid that results in the reduction or loss of its biological properties. Denaturation is caused by heat, chemicals, and extremes of pH. The differences between raw and boiled eggs are largely a result of denaturation.
3. To add another isotope to a fissile material to make it unsuitable for use in a nuclear weapon.