to leave behind: to go away from someone or something, or to let it stay behind, remain, or be given up
This is a strengthened form of the ordinary verb for leaving. The prefix adds the sense of leaving something firmly in place or fully behind you, so the word covers a wide arc: walking away from a town or a group of people, leaving a person on their own, leaving heirs when you die, giving something up for good, and keeping a portion in reserve.
What holds all of these together is a single picture: one party moves on, or takes a decisive step, and something is left where it was. Whether that leftover is a place, a person, a possession, or a surviving remnant, the word describes the same act of separation from the speaker's side.
The shades matter because English forces a choice the Greek does not. The same verb that means a neutral departure from a town can also mean a wholehearted renouncing of everything you own, or the deliberate sparing of a faithful few. Context, not the word itself, tells you which weight to hear.