to live, to be alive; and, by extension, the true life that God has and gives.
At its root this word means simply to be alive rather than dead. It covers a person breathing and walking around, a widow still living while her husband is gone, someone shown to be alive after others thought him dead. From there it stretches in two directions that matter for the whole New Testament.
First, it describes how a person lives, the shape and direction of a life, not just the fact of it. To live to oneself, to live by the rules of the world, to live in a way that pleases God: all of these use this one verb. Being alive and living a certain kind of life are not split into separate words here, so the same term that means breathing also means conducting your life.
Second, and most distinctively, it names a deeper life that belongs first to God. God is repeatedly called the One who lives, the living God, in contrast to idols that are dead and powerless. Because God lives, he can give life, and the New Testament uses this verb for the life he gives: rising from the dead, and the lasting life that comes through trusting Christ. So the same word runs from an ordinary heartbeat all the way to resurrection, and the writers move along that range on purpose.