Select the best one-word substitute for the phrase: "A person famous and respected within a particular sphere."

Introduction / Context:
This question checks your knowledge of one-word substitutes in English vocabulary. The phrase describes a person who is both famous and respected, but only within a particular field, profession, or area of activity. The aim is to choose the single word that most accurately and commonly expresses this meaning in standard English usage.

Given Data / Assumptions:

- Phrase: A person famous and respected within a particular sphere. - Options: eminent, obscure, despotic, imperative. - Only one option should carry the idea of fame and respect in a specific domain. - The context is typically professions or areas like science, art, politics, or scholarship.

Concept / Approach:
The adjective eminent refers to someone who is famous, distinguished, and highly respected in a particular profession or sphere. For example, an eminent scientist or an eminent lawyer is widely recognised for outstanding work. By contrast, obscure means not well known, despotic refers to a ruler who exercises power in a cruel or arbitrary way, and imperative is either an adjective meaning absolutely necessary or a grammatical term. Thus, only eminent matches the idea in the phrase.

Step-by-Step Solution:
Step 1: Focus on the key ideas in the phrase: famous, respected, and within a particular sphere. Step 2: Examine eminent. It is commonly used for well known and highly regarded people in a given field, such as eminent doctors or eminent historians. Step 3: Look at obscure, which describes people or things that are little known or hidden from public notice, the opposite of famous. Step 4: Consider despotic, which refers to oppressive rule or behaviour, not to fame and respect. Step 5: Check imperative, which usually means essential or urgent, and also functions as a grammatical label for command forms. Step 6: Conclude that eminent is the only word that matches all parts of the given phrase.

Verification / Alternative check:
Insert each option into a sample sentence. The phrase He is an eminent cardiologist fits perfectly and means he is widely respected in cardiology. He is an obscure cardiologist would mean the opposite. Calling someone a despotic cardiologist or an imperative cardiologist is unnatural and either produces nonsense or completely changes the intended meaning. This confirms that eminent is the correct choice.

Why Other Options Are Wrong:
Obscure contradicts the idea of being famous, because it refers to being unknown or not clearly seen. Despotic conveys harsh, tyrannical behaviour and has no built in sense of admiration. Imperative describes necessity or command, neither of which relates to being respected in a professional sphere. None of these options combine both fame and respect in a particular area, so they cannot be accepted as correct substitutes.

Common Pitfalls:
Some test takers choose unfamiliar words at random, assuming that the hardest word must be correct. Others may vaguely remember despotic and imperative as important sounding and confuse importance with respect. A more reliable method is to learn one-word substitutes with example phrases that show their typical usage. When you see eminent together with titles like scholar or judge in reading materials, it becomes easier to recall its meaning accurately in exams.

Final Answer:
eminent is the correct one-word substitute for a person who is famous and respected within a particular sphere.