Choose the correct one-word substitution for "a drug or other substance that produces sleep".

Introduction / Context:
This vocabulary question asks you to choose a one-word term for a substance that produces sleep. Such words are often used in medicine, pharmacology, and literature. The correct answer should specifically highlight the sleep inducing effect rather than general dulling or other medical properties.

Given Data / Assumptions:
The phrase is:

• A drug or other substance that produces sleep.

The options are:

• Soporific
• Depressant
• Narcotic
• Antiseptic

We assume common English definitions used in standard dictionaries.

Concept / Approach:
Soporific is the precise word used to describe something that causes or tends to cause sleep or drowsiness. Depressant is a broader term for a drug that lowers the activity of the central nervous system, which may not always focus only on sleep. Narcotic is used for drugs that relieve pain and can cause stupor, but has a legal and medical range of meanings not limited to sleep. Antiseptic refers to a substance that prevents infection, not sleep. Therefore, soporific best fits the definition given in the question.

Step-by-Step Solution:
Step 1: Focus on the key part of the phrase: produces sleep. Step 2: Examine Soporific. It directly means tending to induce drowsiness or sleep. Even a boring lecture can be described as soporific because it makes people sleepy. Step 3: Examine Depressant. This is a general medical term for a substance that lowers the rate of vital body functions. It may relax or calm but is not defined solely by its ability to produce sleep. Step 4: Examine Narcotic. This refers to drugs that relieve pain and may cause stupor or unconsciousness. The focus is on pain relief and altered consciousness, not specifically on normal sleep. Step 5: Examine Antiseptic. This refers to a substance that prevents infection by stopping the growth of microorganisms and has nothing to do with sleep. Step 6: Therefore, among the options, Soporific most accurately captures the idea of a sleep producing substance.

Verification / Alternative check:
We can verify by using the words in example sentences. A medical textbook might say The doctor prescribed a mild soporific to help the patient sleep, which directly links soporific with sleep. Depressant drugs may be described in terms of slowing heart rate or reducing anxiety, and narcotics in terms of strong pain relief and addiction risk. Antiseptic is used in contexts like antiseptic cream, focusing on infection control. This comparison confirms that soporific is the targeted term.

Why Other Options Are Wrong:
Depressant is wrong because not every depressant is intended primarily to make you sleep; some reduce anxiety or agitation without inducing deep sleep. Narcotic is wrong because it emphasises pain relief and stupor and does not specifically denote a normal sleep producing agent. Antiseptic is clearly unrelated because it deals with killing germs rather than affecting the nervous system. Only soporific directly and primarily refers to something that induces sleep.

Common Pitfalls:
Students sometimes confuse narcotic, sedative, and soporific since all can be associated with drowsiness. The key is that soporific directly describes a sleep inducing effect, while narcotic and depressant are broader categories with additional meanings. Another pitfall is picking a familiar word like depressant without checking if it matches the exact definition given. Reading the phrase carefully and matching it to the most precise term prevents such mistakes.

Final Answer:
The correct one-word substitution is Soporific.