Identify the most appropriate meaning of the given idiom.
Bread and butter

The correct option is Means of livelihood.

Explanation:
The idiom "Bread and butter" refers to a person's main source of income, occupation, or financial support that provides them with the basic necessities of life.

Detailed Analysis of Options:
• Comfortable living: Refers to a life of ease or luxury, whereas the idiom specifically refers to basic income and sustenance.
• Means of livelihood: Correct. This accurately describes the job, key work, or primary source of earning that sustains someone's living.
• The breakfast: This is a literal interpretation of the food items "bread" and "butter," which is not the metaphorical meaning of the idiom.
• Money making: Refers generally to generating money or profits, but misses the core concept of basic daily sustainment and primary livelihood.