bread and butter

Short definition from Wiktionary

Noun

1. 1
   That which is central or fundamental, as to one's business, survival, or income; a staple or cornerstone.
2. 2
   The basic requirements of living, such as food and housing.
3. 3
   Used other than figuratively or idiomatically: see bread, butter.

Interjection

1. 1
   Said when two people walking together are temporarily separated by an obstacle in order to indicate that they belong together.
2. 2
   A general saying used to ward off bad luck
3. 3
   A saying specifically used to ward off bad luck when separating hands to walk either side of a tree

Adjective

1. 1
   Relating to basic sustenance or the requirements for everyday living.
2. 2
   Used other than figuratively or idiomatically: see bread, and, butter.