1
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Phrase(s): someone’s bread and butter
Fig. someone’s basic income; someone’s livelihood—the source of one’s food. • I can’t miss another day of work. That’s my bread and butter. • I worked as a bartender for a year, and it was the tips that were my bread and butter.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
1. The essential, sustaining element, as in The quality of the schools is the bread and butter of town property values. This idiom alludes to a basic food, bread spread with butter. [c. 1700] 2. Means of livelihood, as in John's job is the family's bread and butter. [First half of 1700s] 3. Ordinary, routine, as in Don't worry about it; this is just a bread and butter assignment. [Second half of 1800s]
American Heritage Idioms