Entirely, heartily, tooth and nail, with might and main. The reference is to a wedge driven home to split wood.
“They were working back and edge for me.” —Boldrewood: Robbery under Arms , ch. ii.
To back and fill. A mode of tacking, when the tide is with the vessel and the wind against it. Metaphorically, to be irresolute.
To back out. To draw back from an engagement, bargain, etc., because it does not seem so plausible as you once thought it. Many horses are unwilling to go out of a stable head foremost, and are backed out.
“Octavius backs out; his caution and reserve come to her rescue.” —C. Clarke: Shakespeare.
To back the field. To bet on all the horses bar one. A sporting term used in betting.
To back the sails. So to arrange them that the ship's way may be checked.
To back up. To uphold, to support. As one who stands at your back to support you.
At the back of. Behind, following close after. Figure from following a leader.
“With half the city at his back.” Byron: Don Juan.
To see his back; to see the back of anything. To get rid of a person or thing; to see it leave
Back the oars or back water is to row backwards, that the boat may move the reverse of its ordinary direction.
On the back of. Immediately after. Figure from soldiers on the march.
To the back, that is, to the backbone, entirely.
To break the back of a thing. To surmount the hardest part.
His back is up. He is angry, he shows that he is annoyed. The allusion is to a cat, which sets its back up when attacked by a dog or other animal.
To get one's back up. To be irritated (See above).
To have his back at the wall. To act on the defensive against odds. One beset with foes tries to get his back against a wall that he may not be attacked by foes behind.
“He planted his back against a wall, in a skilful attitude of fence ready with his bright glancing rapier to do battle with all the heavy fierce unarmed men, some six or seven in number.” —Mrs. Gaskell: The Poor Clare, iii.
To set one's back up. (See above.) “That word set my back up.” Dame Huddle's Letter (1710).
To turn one's back on another. To leave, forsake, or neglect him. To leave one by going away.
“At length we ... turn our backs on the outskirts of civilisation.” —Tristram: Moab, ii. 19.
Behind my back. When I was not present. When my back was turned.
Laid on one's back. Laid up with chronic ill-health; helpless. Figure from persons extremely ill.
Thrown on his back. Completely worsted. A figure taken from wrestlers.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894