Real Dictionary

back adverb uses
If someone or something is back in a particular state, they were in that state before and are now in it again.
If something is or comes back, it is fashionable again after it has been unfashionable for some time.
If you give or put something back, you return it to the person who had it or to the place where it was before you took it. If you get or take something back, you then have it again after not having it for a while.
If you go back somewhere, you return to where you were before.
If you move back, you move in the opposite direction to the one in which you are facing or in which you were moving before.
If you put a clock or watch back, you change the time shown on it so that it shows an earlier time, for example when the time changes to winter time or standard time.
If you write or call back, you write to or phone someone after they have written to or phoned you. If you look back at someone, you look at them after they have started looking at you.
You can say that you go or come back to a particular point in a conversation to show that you are mentioning or discussing it again.

Back in American English
river in N Canada, flowing northeast into the Arctic Ocean: c. 600 mi (966 km)

back in American English 1
the part of the body opposite to the front; in humans and many other animals, the part to the rear or top reaching from the nape of the neck to the end of the spine
noun: the rear part of the human body, extending from the neck to the lower end of the spine

back in American English 2
a vat or tub used in certain industrial processes
adverb: at, to, or toward the rear; backward

back in American English 3
noun: a large tub, vat, or cistern used by dyers, brewers, distillers, etc., to hold liquids

back in British English 1
noun: the posterior part of the human body, extending from the neck to the pelvis

back in British English 2
noun: a large tub or vat, esp one used by brewers

back opposite of front; noun and adjective uses
A person's or animal's back is the part of their body between their head and their legs that is on the opposite side to their chest and stomach.
Back is used to refer to the side or part of something that is towards the rear or farthest from the front.
The back of a book is the part nearest the end, where you can find the index or the notes, for example.
The back of a chair or sofa is the part that you lean against when you sit on it.
The back of something is the side or part of it that is towards the rear or farthest from the front. The back of something is normally not used or seen as much as the front.
The back of something such as a piece of paper or an envelope is the side which is less important.
countable noun: In American football, a back is a player who stands behind the front line, runs with the ball and attacks rather than defends.
countable noun: In team games such as football and hockey, a back is a player who is concerned mainly with preventing the other team from scoring goals, rather than scoring goals for their own team.
phrase: If two or more things are done back to back, one follows immediately after the other without any interruption.
singular noun: You can use back in expressions such as round the back and out the back to refer generally to the area behind a house or other building.
uncountable noun: You use back in expressions such as out back to refer to the area behind a house or other building. You also use in back in American English to refer to the rear part of something, especially a car or building.

back verb uses
verb: If a building backs onto something, the back of it faces in the direction of that thing or touches the edge of that thing.