What is the greek word for life force?

There isn't one single perfect Greek word for "life force" in the way that term is used in modern contexts (e.g., vital energy, *qi*, etc.). The concept is expressed differently depending on the philosophical or religious system. However, several words and phrases come close, depending on the nuance you want to convey:

* ψυχή (psyche): This is probably the closest single word. While often translated as "soul," psyche encompassed a broader concept encompassing the mind, spirit, and life principle itself. It's the closest equivalent to a "life force" that animates a being.

* πνεῦμα (pneuma): This word means "breath," "spirit," or "wind," but it was also associated with the vital breath that sustains life. Think of it as the animating breath or spirit that gives life.

* ζωή (zōē): This simply means "life," but in certain philosophical contexts, it could imply the underlying principle of life itself.

* δύναμις (dynamis): This means "power" or "ability," and could be used to refer to the inherent power or energy that sustains life.

Therefore, depending on the context, ψυχή (psyche) is likely the best single-word approximation, though πνεῦμα (pneuma) is a strong contender, particularly if the emphasis is on the breath-like aspect of the life force. No single word perfectly captures the multifaceted modern concept of "life force," however.