In English vocabulary, choose the one word that best substitutes the given phrase: A conclusion or agreement done or reached decisively and with authority.

Introduction / Context:
This question belongs to the one word substitution category, where you must replace a descriptive phrase with a single precise word. The phrase here describes a conclusion or agreement that has been reached decisively and with authority, leaving little room for doubt or further change. Questions like this are common in government and banking exams because they measure how well you can match nuanced meanings with exact vocabulary items.

Given Data / Assumptions:

• Descriptive phrase: A conclusion or agreement done or reached decisively and with authority.
• Options: precise, definitive, reliable, specific.
• We must find the word that encapsulates the idea of final, authoritative and conclusive.
• Only one option should fully capture this sense.

Concept / Approach:
The adjective definitive means final, decisive or authoritative, something that is regarded as the most complete and reliable version. A definitive agreement, for example, is one that settles the matter completely. Precise means exact or accurate in detail but does not always imply finality. Reliable refers to something that can be trusted, and specific simply means clearly defined or particular. Among the options, definitive is the only one that combines the ideas of decisiveness and authoritative final status, so it is the correct one word substitute.

Step-by-Step Solution:
Step 1: Interpret the phrase. It refers to a conclusion or agreement that is final and authoritative. Step 2: Consider precise. It is about accuracy in detail, not necessarily about authority or finality. Step 3: Consider definitive. This word means serving as the final, most authoritative or conclusive form of something. Step 4: Consider reliable. It means dependable, which is related to trustworthiness but not directly to the idea of a final decision. Step 5: Consider specific. It indicates that something is clearly defined or particular, again not emphasising decisiveness.

Verification / Alternative check:
Consider example phrases: definitive judgment, definitive agreement, definitive version. All suggest the final, official or most complete form. In contrast, you might speak of a precise measurement or a reliable source, which relate to accuracy and trustworthiness, not closure of debate. Specific answer simply indicates detail but not authority. Therefore, definitive is the best match for the original phrase, as confirmed by dictionary definitions and common collocations in formal writing.

Why Other Options Are Wrong:

• precise: Emphasises exactness and detail, but does not carry the sense of final and authoritative in the way definitive does.
• reliable: Focuses on trust and dependability, not on closing a matter decisively.
• specific: Points to clear and particular reference but does not indicate that the issue is conclusively settled.

Common Pitfalls:
Students often confuse precise and definitive because both can appear in academic or legal contexts. However, precise answers can still be revised, while definitive answers are usually final. Another mistake is choosing reliable simply because it sounds positive, without checking whether it matches the requirement of being conclusive. To avoid these errors, pay close attention to the exact wording in the phrase, especially terms like decisively and with authority, which strongly point towards definitive.

Final Answer:
The correct one word substitute is definitive, which means a final and authoritative conclusion or agreement.