1. the food or money a person needs in order to live
a person's means of subsistence: one's ( s.o. 's) daily bread.
Мой отец тоже остался без работы. И встала проблема -чем заняться? Как заработать на хлеб насущный? (Рыбаков 1). My father was also out of work. The question was, what could he do for a living? How could he earn his daily bread? (1a).
2. that which is most important, essential, that which some person (group etc) cannot do without
lifeblood.
From the Bible (Matt. 6:11).
Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. С.И. Лубенская. 2004.