Out of the four alternatives, choose the one word which can be substituted for the given description. A person's peculiar habit.

Introduction:
One word substitution questions check your ability to recall precise vocabulary that captures a full description in a single term. The description here talks about a peculiar habit of a person, which suggests an individual quirk or distinctive behavioural pattern. The correct choice must reflect this nuance, not just any general quality or ability.

Given Data / Assumptions:
- Description: "A person's peculiar habit."
- Options: Trait, Idiosyncrasy, Idiolect, Talent.
- We assume the habit is something unusual or distinctive, not merely a neutral characteristic.

Concept / Approach:
The word "idiosyncrasy" is used in English to describe a person's distinctive or odd habit, mannerism, or way of behaving that sets them apart from others. It is stronger than "trait", which can refer to any characteristic, and different from "idiolect", which relates to language, or "talent", which means a special ability. The correct answer must closely match the idea of a peculiar habit.

Step-by-Step Solution:
Step 1: Recall the definition of "idiosyncrasy": a way of behaving, thinking, or feeling that is unusual and specific to one person.Step 2: Note that it is commonly used for peculiar habits, such as a person always arranging objects in a particular way.Step 3: Compare this with "trait", which is any distinguishing quality, like honesty, height, or eye colour, and is not necessarily peculiar.Step 4: Look at "idiolect". This term refers to an individual's unique way of using language, vocabulary, and grammar, not to habits in general.Step 5: Consider "talent", which describes a natural ability or skill, usually something positive and not necessarily peculiar. Therefore, "idiosyncrasy" is the best match.

Verification / Alternative check:
Use each word in a sentence: "One of his idiosyncrasies is talking to plants", clearly describes a peculiar habit. "One of his traits is patience" just describes a general characteristic. "His idiolect includes many local expressions" shows language use, and "She has a talent for music" refers to ability. Only "idiosyncrasy" naturally expresses the idea of a strange or distinctive personal habit.

Why Other Options Are Wrong:
Option A, Trait, is too broad and neutral; not every trait is peculiar. Option C, Idiolect, is restricted to a person's individual speech patterns and does not cover non linguistic habits. Option D, Talent, refers to special skill, especially in arts or sports, and is not about habits at all. Option B, Idiosyncrasy, specifically means a peculiar habit or mannerism of an individual, so it is the only precise answer.

Common Pitfalls:
Students may choose "trait" because it is a common word, but exam setters aim for more precise vocabulary. Others might be tempted by "idiolect" because it looks similar to "idiosyncrasy", but that word belongs to the field of linguistics. To avoid such confusion, it is helpful to link "idiosyncrasy" in your memory with examples of odd personal habits, such as always tapping the table three times before eating.

Final Answer:
The one word substitute for "a person's peculiar habit" is Idiosyncrasy.