In English vocabulary, select the synonym that best expresses the meaning of the word "bounder".

Introduction / Context:
This is a vocabulary question about the word "bounder". It asks you to choose the option that is closest in meaning to this word. "Bounder" is a somewhat old fashioned English term that still appears in literature and exams. It typically refers to a man whose behaviour is socially unacceptable, rude, or lacking in manners. To answer correctly, you must know or infer this meaning and then match it with the most suitable option among the choices given.

Given Data / Assumptions:

• The target word is "bounder".
• The options are "lout", "mediocre", "done", and "decorous".
• Exactly one option must be the closest synonym in meaning.
• The context is social behaviour and character, not physical boundaries.

Concept / Approach:
"Bounder" is used to describe a person, usually a man, whose manners and conduct are considered disgraceful, rude, or socially offensive. It often suggests someone who does not respect social norms or polite behaviour. When you look at the options, you need to find a word that is also used for an ill mannered or boorish person. Words related to quality level, completeness, or politeness will not match. The strategy is to think of the semantic field of behaviour and manners and ignore options that clearly belong to different domains.

Step-by-Step Solution:
Step 1: Recall that "bounder" refers to a socially unacceptable, ill mannered, or obnoxious person. Step 2: Examine "lout". A "lout" is a rude, aggressive, or uncouth man, someone who behaves in a bad manner. Step 3: Examine "mediocre". This word means average or of only moderate quality. It describes quality, not behaviour or manners. Step 4: Examine "done". This simply means finished or completed, and has nothing to do with personality or behaviour. Step 5: Examine "decorous". "Decorous" means showing good taste and proper, polite behaviour. Step 6: Compare all options with the idea of an ill mannered man. Only "lout" matches the sense of rude and socially offensive behaviour.

Verification / Alternative check:
A quick way to verify is to imagine a sentence from a novel: "Everyone at the party thought he was a complete bounder." If we replace "bounder" with "lout", the sentence still makes sense: "Everyone at the party thought he was a complete lout." Replacing with "mediocre" or "done" makes no sense, and "decorous" would be the opposite meaning, since it implies polite and proper behaviour. This substitution exercise clearly confirms that "lout" is the intended synonym.

Why Other Options Are Wrong:
"Mediocre" is wrong because it relates to average or second rate quality, not to social behaviour. "Done" is wrong because it refers to completion of an action or task and is unrelated to descriptions of character. "Decorous" is particularly wrong because it suggests good manners and propriety, which is the opposite of what "bounder" implies. Since "bounder" is negative and "decorous" is positive, they cannot be synonyms.

Common Pitfalls:
A common error is to select a word just because it appears more familiar, without carefully considering its meaning. Many candidates know "mediocre" and "done" but may be less certain about "lout" and "bounder". However, exams often test precisely such less common but important words. Another pitfall is assuming that a word with a formal or elegant sound like "decorous" must be correct, when in fact the original word has a negative tone. Always pay attention to whether the tone is positive or negative and whether it fits the context of the word being tested.

Final Answer:
The synonym that best expresses the meaning of "bounder" is lout.