Explanation:

- *The phrase "a mode of behavior or way of thought peculiar to an individual" aligns with the definition of "idiosyncratic." This word signifies a trait or habit unique to a person but does not imply any abnormality.*

- Option 1: Singular

Means unique or one of a kind, but doesn't quite capture the idea of personal peculiar behavior.

- ? Option 2: Idiosyncratic

Refers to a distinctive or peculiar feature or characteristic unique to an individual.

- Option 3: Cynical

Means having a belief that people are motivated by self-interest; distrustful of human sincerity and integrity.

- Option 4: Idiotic

Refers to something that is very stupid or foolish, which doesn't fit the context.