A staple or necessary food, especially bread. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "staff of life" in a sentence
"Most of the time only one-fourth pound of bread for two days was allowed; and the soggy black peasant's bread is the staff of life in Russia – it is not a "trimming" like our American bread."