In this vocabulary based odd one out question, you must select the word whose meaning is opposite in sense to the other three words Adamant, Stubborn, Tenacious and Lenient.

Introduction / Context:
This is a verbal ability and vocabulary question that asks you to find the odd one out among four English words. The main skill tested is recognizing synonyms and antonyms. Three of the words express a similar idea, while one word expresses an opposite or significantly different idea. Such questions are commonly used in aptitude tests to check word meaning and nuance.

Given Data / Assumptions:

• The words given are Adamant, Stubborn, Tenacious and Lenient.
• We assume general English usage and standard dictionary meanings.
• The goal is to group words by similarity of meaning.

Concept / Approach:
The strategy is to understand the meanings of all four words. Adamant, Stubborn and Tenacious all indicate a strong unwillingness to change one opinion or an ability to hold firmly to a position or goal. Lenient, however, means tolerant, permissive or not strict. Thus, Lenient represents the opposite attitude in comparison to the other three words, which describe a kind of firm or unyielding behavior.

Step-by-Step Solution:
Step 1: Adamant describes someone who is firm, unshakable and not willing to change opinions or decisions easily.Step 2: Stubborn also refers to a person who refuses to change their mind or behavior, often even when it is unreasonable to stay fixed.Step 3: Tenacious means holding on firmly, showing great determination or persistence, which again reflects a resolute and firm attitude.Step 4: Lenient means mild, tolerant, soft or permissive. A lenient person is flexible and less strict in enforcing rules or demands.Step 5: Clearly, Adamant, Stubborn and Tenacious all describe firmness and rigidity, while Lenient describes the opposite, a more forgiving and flexible nature. Therefore, Lenient is the odd one out.
Verification / Alternative check:
To verify, you can think of simple antonym pairs. The opposite of strict, firm or harsh is lenient or gentle. Since Adamant, Stubborn and Tenacious cluster around firmness, their natural opposite would be Lenient. Thus, looking at common usage and dictionary definitions strongly confirms that Lenient is the only word that does not belong with the others.

Why Other Options Are Wrong:
Adamant is not the odd one out because its meaning of being unyielding aligns closely with Stubborn and Tenacious.
Stubborn also fits the firm and unchanging theme and therefore is not unique among the options.
Tenacious, which conveys determination and firm grip, also belongs in the same meaning group as Adamant and Stubborn.

Common Pitfalls:
Students sometimes confuse Tenacious with a positive quality and Stubborn with a negative one, but both still indicate firmness. The odd one out is not chosen based on positive or negative connotation but on similarity of meaning. Another mistake is to think that Adamant is different because it is less commonly used, but vocabulary frequency is not relevant here; meaning is the key criterion.

Final Answer:
The only word that expresses a contrasting idea to the other three is Lenient, so Lenient is the odd one out.