The following is a list of synonyms for the word life that are listed in a dictionary of synonyms and antonyms that I have: Existence, animation, vitality, source, vivacity, essence, origin, manner, conduct, custom, principle, nature, breath, being, entity, endurance, duration. To me some of them don't make sense, but those are the words that were listed in the book as synonyms for life. I hope you can find the word you are most comfortable with.
I'd also say existence, being, or time
You could use "existence" - it's often used as a synonym although strictly not quite the same. There is also "vitality" meaning life force/energy.
I went into Microsoft Word and used the synonym option. This is what it gave me: Verve, existence, being, time, living, years, days.
Depending upon where it is used maybe "verve" would work.
Took the words right out of my mouth, Existence would sum it up in a nutshell.