1. Adaptive state characterised by diminished effects of a particular dose of a substance: the process leading to tolerance is called "adaptation".

2. In food toxicology, dose that an individual can tolerate without showing an effect.

3. Ability to experience exposure to potentially harmful amounts of a substance without showing an adverse effect.

4. Ability of an organism to survive in the presence of a toxic substance: increased tolerance may be acquired by adaptation to constant exposure.

5. In immunology, state of specific immunological unresponsiveness.