Define a tranquillizer.

Explanation

**Step-by-Step Solution:**

1. **Definition of Tranquilizer**: A tranquilizer is a type of medication that is primarily used to reduce anxiety and induce a sense of calmness in individuals.

2. **Function**: Tranquilizers help in alleviating symptoms associated with stress, mental disorders, fear, and tension. They are often prescribed for conditions such as anxiety disorders and other mental health issues.

3. **Mechanism of Action**: These medications work by affecting certain neurotransmitters in the brain. Specifically, they inhibit the action of enzymes that are involved in the production of stress-related hormones like adrenaline and noradrenaline.

...