In the following question, out of the four alternatives, select the one word which is the best substitute for the given definition. A sheath for the blade of a sword.

Introduction / Context:
This one word substitution question tests vocabulary connected with historical objects and weapons, often encountered in literature and general knowledge. The definition given is a sheath for the blade of a sword. The correct answer must name the specific protective covering into which a sword is placed when not in use. The distractor options are verbs related to uncovering or revealing, which are conceptually opposite to the idea of covering or protecting.

Given Data / Assumptions:

• Definition: A sheath for the blade of a sword.
• Options: Scabbard, Denude, Divulge, Expose.
• We assume standard English usage found in novels, history, and competitive exams.
• The correct word should be a noun naming a physical object, not a verb describing an action.

Concept / Approach:
The technical term for the protective case that holds a sword, sabre, or similar weapon is scabbard. This word appears in historical fiction, military descriptions, and museum contexts. The other options denude, divulge, and expose are verbs. Denude means to strip something of its covering, divulge means to reveal information, and expose means to make visible or leave unprotected. All of these describe actions of removing protection rather than providing it. The approach is to recognise that the definition clearly points to an object and to select the only noun that matches this purpose.

Step-by-Step Solution:
Step 1: Focus on the keywords sheath and blade of a sword, which indicate a protective case used to cover and carry the weapon.Step 2: Recall the standard term scabbard, which is exactly defined as a sheath for a sword or dagger.Step 3: Note that Denude, Divulge, and Expose are all verbs that describe removing cover, revealing, or uncovering something.Step 4: Since the question asks for a sheath, that is, the cover itself, these verbs cannot fit.Step 5: Therefore, Scabbard is the only option that matches both the grammatical form and the meaning of the definition.

Verification / Alternative check:
We can verify by building simple sentences. A knight drew his sword from its scabbard is a standard English sentence and clearly refers to a sword being pulled out of its protective case. If we try to use denude, divulge, or expose in place of scabbard, the sentence becomes meaningless, because these words do not refer to an object. Moreover, dictionaries and historical descriptions consistently define scabbard as a sheath for a sword or a blade. This cross check confirms that scabbard is the correct one word substitute.

Why Other Options Are Wrong:
Denude: This means to strip something of its covering, for example denuding a forest of trees. It is an action, not a thing, and runs opposite to the idea of a sheath. Divulge: This verb means to make known something private or secret, such as divulging information, which relates to knowledge, not physical objects. Expose: This means to leave something without protection or to reveal it to view. Again, it describes an action that removes cover, while a scabbard is the cover itself. None of these verbs can be used as the name of the sheath of a sword.

Common Pitfalls:
Some candidates may not be familiar with the word scabbard because it is more common in older literature than in modern speech. Others may pay attention only to the general idea of covering and mistakenly select a verb that sounds like it might be related. A reliable exam strategy is to first decide whether the definition describes a thing, a person, or an action. Here, a sheath is clearly a thing, so only a noun can be correct. Among the options, scabbard is the only noun and also matches the definition perfectly.

Final Answer:
The one word substitute for a sheath for the blade of a sword is Scabbard.