back / bak/ • n. 1. the rear surface of the human body from the shoulders to the hips: he lay on his back ∎  the corresponding upper surface of an animal's body. ∎  the part of a chair against which the sitter's back rests. ∎  the part of a garment that covers a person's back. ∎  a person's torso or body regarded in terms of wearing clothes: all he owned were the clothes on his back. ∎  a person's back regarded as carrying a load or bearing an imposition: they wanted the government off their backs.2. the side or part of something that is away from the spectator or from the direction in which it moves or faces; the rear: at the back of the hotel is a secluded garden ∎  [in sing.] the position directly behind someone or something: she unbuttoned her dress from the back. ∎  the side or part of an object opposed to the one that is normally seen or used; the less active, visible, or important part of something: write on the back of a postcard3. a player in a field game whose initial position is behind the front line: their backs showed some impressive running and passing.• adv. 1. toward the rear; in the opposite direction from the one that one is facing or traveling: she moved back a pace she walked away without looking back. ∎  expressing movement of the body into a reclining position: he leaned back in his chair sit back and relax. ∎  at a distance away: I thought you were miles back the officer pushed the crowd back. ∎  (back of) behind: he knew that other people were back of him.2. expressing a return to an earlier or normal condition: she put the book back on the shelf drive to Montreal and back I went back to sleep ∎  fashionable again: sideburns are back.3. in or into the past: he made his fortune back in 1955. ∎  at a place previously left or mentioned: the folks back home are counting on him.4. in return: they wrote back to me.• v. 1. [tr.] give financial, material, or moral support to: he had a newspaper empire backing him go up there and tell them—I'll back you up.| ∎  bet money on (a person or animal) winning a race or contest: he backed the horse at 33–1. ∎  be in favor of: over 97 percent backed the changes. ∎  supplement in order to reinforce or strengthen: U.S. troops were backed up by forces from European countries.2. (esp. in popular music) provide musical accompaniment to (a singer or musician): brisk guitar work backed by drums, bass, fiddle, and accordion.3. [intr.] walk or drive backward: she tried to back away backing down the stairs | fig. the administration backed away from the plan | [tr.] he backed the Mercedes into the yard. • adj. 1. of or at the back of something: the back pocket of his jeans. ∎  situated in a remote or subsidiary position: back roads.2. (esp. of wages or something published or released) from or relating to the past: she was owed back pay.3. directed toward the rear or in a reversed course: back currents.4. Phonet. (of a sound) articulated at the back of the mouth.PHRASES: back and forth to and fro.someone's back is turned someone's attention is elsewhere: he kissed her quickly, when the landlady's back was turned.the back of one's mind used to express that something is in one's mind but is not consciously thought of or remembered: she had a little nagging worry at the back of her mind.back the wrong horse make a wrong or inappropriate choice.behind someone's back without a person's knowledge and in an unfair or dishonorable way: Carla made fun of him behind his back.get (or put) someone's back up make someone annoyed or angry.in back at the back of something, esp. a building: my dad demolished an old shed in back of his barn.know something like the back of one's hand be entirely familiar with a place or route.on one's back full-length on the ground: he slipped off the heap and landed flat on his back.turn one's back on ignore (someone) by turning away. ∎  reject or abandon: she turned her back on her career to devote her life to animals.with one's back to (or up against) the wall in a desperate situation; hard-pressed.PHRASAL VERBS: back down withdraw a claim or assertion in the face of opposition: the contenders backed down from their original pledge.back off draw back from action or confrontation: they backed off from fundamental reform of the system. ∎ another way of saying back down.back out withdraw from a commitment: if he backs out of the deal they'll sue him.back up1. (of vehicles) form a line due to congestion: the traffic began to back up.2. (of running water) accumulate behind an obstruction.back something up Comput. make a spare copy of data or a disk.

back1 back number a person whose methods or ideas are regarded as out of date, and who is no long seen as important. In literal use, this was originally the issue of a periodical before the current one.
back of beyond a term (first recorded in Sir Walter Scott's The Antiquary, 1816, as a humorous phrase for some very out of the way place), used in Australia for the far inland regions remote from large towns or closely settled districts, the backblocks.
back of Bourke the remote and sparsely populated inland of Australia; Bourke is a town in New South Wales.
back-seat driver someone who lectures or criticizes the person who is actually in control, from the idea of a passenger in the back of a car giving the driver unwanted advice.
back slang slang in which words are spoken as though they were spelled backwards (e.g. redraw for warder).
back to basics a political catchphrase of the early 1990s, embodying a conscious return to what are seen as fundamental principles of self-respect, decency, and honesty. The use of the phrase derived from a speech made by John Major, then Prime Minister, to the Conservative Party Conference in 1993.
put someone's back up make someone annoyed or angry, in allusion to the idea of a cat's arching its back in anger.

back. The lower or rear part of the resonant box of str. instr. The strings are extended across the upper part, the belly or ‘table’. The back has no sound holes; its primary function is to be reverberated by the air waves generated by the belly as it vibrates under the str. Usually made of maple, pear, or other hard wood.

back.
1. Principal rafter in a roof.

2. Top or visible part of e.g. a slate.

3. Rear part of something, or its hidden side.

back1 hinder surface. OE. bæc, OS., ON, bak :- Gmc. *bakam.
Hence back vb. XIV; adj. XVI, with superl. backmost XVIIII. So backside XV (prob. Scand., cf. Norw. bakside).