Back v. t. [imp. & p. p. Backed p. pr. & vb. n. Backing.]
 1. To get upon the back of; to mount.
    I will back him [a horse] straight.   --Shak.
 2. To place or seat upon the back. [R.]
 Great Jupiter, upon his eagle backed,
 Appeared to me.   --Shak.
 3. To drive or force backward; to cause to retreat or recede; as, to back oxen.
 4. To make a back for; to furnish with a back; as, to back books.
 5. To adjoin behind; to be at the back of.
    A garden . . . with a vineyard backed.   --Shak.
    The chalk cliffs which back the beach.   --Huxley.
 6. To write upon the back of; as, to back a letter; to indorse; as, to back a note or legal document.
 7. To support; to maintain; to second or strengthen by aid or influence; as, to back a friend. “The Parliament would be backed by the people.”
    Have still found it necessary to back and fortify their laws with rewards and punishments.   --South.
    The mate backed the captain manfully.   --Blackw. Mag.
 8. To bet on the success of; -- as, to back a race horse.
 To back an anchor Naut., to lay down a small anchor ahead of a large one, the cable of the small one being fastened to the crown of the large one.
 To back the field, in horse racing, to bet against a particular horse or horses, that some one of all the other horses, collectively designated “the field”, will win.
 To back the oars, to row backward with the oars.
 To back a rope, to put on a preventer.
 To back the sails, to arrange them so as to cause the ship to move astern.
 To back up, to support; to sustain; as, to back up one's friends.
 To back a warrant Law, is for a justice of the peace, in the county where the warrant is to be executed, to sign or indorse a warrant, issued in another county, to apprehend an offender.
 To back water Naut.,  to reverse the action of the oars, paddles, or propeller, so as to force the boat or ship backward.