bread and butter
• maintenance, livelihood, source of income
• habitual, routine, usual; practical, material
• the bread and butter of a person or organization is the activity or work that provides their main source of income.
• the bread-and-butter issues, questions, or problems are the ones that are the most basic and important.
bread and butter letter
• thank you letter, thank you note thanking a person for their hospitality
quarrel with one's bread and butter
• repine, be unhappy, be not satisfied, be discontented