the train backed into the station; the horse refuses to back
2
To support.
I back you all the way; which horse are you backing in this race?
3
(of the wind) To change direction contrary to the normal pattern; that is, to shift anticlockwise in the northern hemisphere, or clockwise in the southern hemisphere.
4
(of a square sail) To brace the yards so that the wind presses on the front of the sail, to slow the ship.
He gave back the money. He needs his money back. He was on vacation, but now he’s back. The office fell into chaos when you left, but now order is back.