In English vocabulary, choose the single word that best substitutes the phrase "One who listens secretly to private conversation".

Introduction / Context:
This one-word substitution question tests your knowledge of a specific term used for a person who secretly listens to private conversations. Such vocabulary items are useful in both everyday English and in exam contexts, as they allow you to express ideas precisely and concisely. Knowing the correct word helps you both in comprehension and in writing tasks.

Given Data / Assumptions:

• Phrase: "One who listens secretly to private conversation".
• Options: Eavesdropper, Encroacher, Eaves bearer, Listener.
• The key idea is "listens secretly" to a conversation meant to be private.
• We assume standard dictionary meanings for each word.

Concept / Approach:
The correct term for a person who secretly listens to others' private conversations without their permission is "eavesdropper". It is formed from the verb "to eavesdrop", which means to listen secretly to what other people are saying. The other options either refer to different concepts or are not standard English words. The approach is to match the phrase exactly to the proper technical word used in English.

Step-by-Step Solution:
Step 1: Focus on the crucial part of the phrase: "listens secretly to private conversation". Step 2: Recall that the verb "eavesdrop" means to listen secretly to people's private talk. Step 3: From that verb, the noun "eavesdropper" naturally means a person who does this secret listening. Step 4: Check "Encroacher": this refers to someone who intrudes on another person's territory, rights, or property, not specifically to secret listening. Step 5: Check "Eaves bearer": this is not a standard English term; it appears to be a distractor. Step 6: Check "Listener": this simply means a person who listens, without the idea of secrecy or privacy, so it is too general.

Verification / Alternative check:
You can verify by looking at example sentences: "The eavesdropper was caught listening at the door" or "It is wrong to be an eavesdropper." In both cases, the word clearly refers to someone secretly listening to private talk. In contrast, "encroacher" appears in sentences about land or rights, and "listener" appears in neutral contexts like "radio listeners". Therefore, "eavesdropper" is the only option that captures the secrecy and privacy aspect in the phrase.

Why Other Options Are Wrong:

• Encroacher: A person who intrudes on another's territory or rights; this is about invasion or intrusion, not specifically listening to conversations.
• Eaves bearer: Not a recognised English word; it is likely a distractor created for the question.
• Listener: A general term for someone who listens, but it does not convey the idea of secrecy or that the conversation is private.

Common Pitfalls:
Students sometimes choose "listener" because it seems directly related to listening, but they forget that the key word in the phrase is "secretly". Another mistake is to be misled by unfamiliar compounds like "eaves bearer". When dealing with one-word substitution questions, always focus on the full meaning, including qualifiers like "secretly" and "private", not just the core noun. Revising vocabulary with clear examples can prevent such confusion.

Final Answer:
The correct one-word substitution is Eavesdropper.