'Fast' in the Bible

Then said Boaz unto Ruth, Hearest thou not, my daughter? Go not to glean in another field, neither pass from hence, but abide here fast by my maidens.

And Ruth the Moabitess said, Yea, he said unto me, Thou shalt keep fast by my young men, until they have ended all my harvest.

So she kept fast by the maidens of Boaz, to glean unto the end of barley harvest and of wheat harvest; and she dwelt with her mother-in-law.