to separate or part: to divide one thing from another, or (of a person) to withdraw and go away
At heart this is a spatial word: it puts distance between two things that were once together. That single act shows up in three everyday settings. Someone can pull two joined things apart, as when Jesus warns that no one should break up a marriage God has joined. A person can pull away and leave, as when Paul goes on from Athens or the Jews are ordered out of Rome. And a husband or wife can walk away from the marriage itself, the situation Paul takes up with the Corinthians.
The same plain verb carries one of the letter to the Romans' great promises. When Paul asks who or what could ever separate believers from the love of Christ, he lists every force that pulls things apart, hardship and danger and death, height and depth, and answers that not one of them can open the smallest gap between God and his people.
Because the word says nothing about how the separation happens, the setting decides its force. In a marriage it can point to a formal split; on a journey it simply means leaving; in Hebrews it pictures Jesus as set apart from sinners, in a class of his own. The reader watches the context to know which kind of parting is meant.