lifeblood

noun

1. the blood, considered as essential to maintain life: to spill one’s lifeblood in war.
2. a life-giving, vital, or animating element: Agriculture is the lifeblood of the country.

noun

1. the blood, considered as vital to sustain life
2. the essential or animating force

n.also life-blood, 1580s, “blood necessary for life,” from life (n.) + blood (n.). Figurative and transferred use is from 1590s.