back · adverb /bæk/Full view
back (RETURNING)
A1 where someone or something was before
Dictionary examples:

When do you go back to college?

I put the tin back in the cupboard.

Learner example:

She [went] back home at once. (Skills for Life (Entry 1); A1; Polish)

back (REPLY)
A2 as a reply or reaction to something
Dictionary examples:

I'm busy at the moment - can I call you back?

I waved to her and she waved back.

Learner example:

Write back to me soon. (Key English Test; A2; Chinese)

back (BEHIND)
B1 in a direction behind you
Dictionary examples:

He sat back on the sofa.

Anna stepped back.

Learner example:

I cried [out], stepping back and falling down. (First Certificate in English; B2; Polish)

back (STATE)
B2 to the state something or someone was in before
Dictionary examples:

It's not badly broken - I'm sure we can put it back together again.

Hopefully things will get back to normal soon.

I was woken by a thunderstorm, and I couldn't get back to sleep.

Learner example:

My life was back to normal. (First Certificate in English; B2; Danish)

back (EARLIER)
B2 at or to an earlier time
Dictionary examples:

We first met back in 1971.

This tradition dates back to the 16th century.

Learner example:

All in all, it is difficult to get bored in Moscow, where you can see buildings which date back to centur[i]es ago. (First Certificate in English; B2; Russian)

back (AWAY FROM)
B2 in a direction away from something
Dictionary examples:

He pulled back the curtain.

The house is set back from the road.

Learner example:

The action of the book takes place in a lonely inn standing back from the road. (First Certificate in English; B2; Polish)

back and forth
C2 in one direction, then the opposite way, then in the original direction again many times
Dictionary example:

He has to travel back and forth between London and Paris every week.

Learner example:

Finally, after much walking back and forth, we found a road which we followed till we got to the town. (Certificate of Proficiency in English; C2; Spanish)

back · noun C /bæk/
the back
A2 the part of something that is furthest from the front or in the opposite direction to the front
Dictionary examples:

He wrote her email address down on the back of an envelope.

Our seats were right at the back of the theatre.

Learner example:

My cousins love mermaids, so each sweater has one on the back. (Key English Test; A2; Spanish)

back
A2 the part of your body from your shoulders to your bottom
Dictionary examples:

back injuries/pain

I've got a bad back.

He lay on his back, staring at the ceiling.

Learner example:

The look on his face stopped me cold, as if someone had just poured freezing water down my back. (Preliminary English Test; B1; French)

back to front
C2 with the back part of something where the front should be
Dictionary example:

You've got your trousers on back to front.

Learner example:

Therefore, the government needs to cut expenditure and as a result of this, health faciliti[es] will only be accessible for rich people. Then we are back to front. (Certificate of Proficiency in English; C2; Dutch)

behind sb's back
C2 If you do something behind someone's back, you do it without them knowing, often in an unfair way.
Dictionary example:

Have they been saying things about me behind my back?

Learner example:

The food must be perfect, too, or else her mother-in-law and my father's sisters will think that she's not a proper wife, and will probably say insulting things about her behind her back. (Certificate of Proficiency in English; C2; Greek)

turn your back on sb/sth
C2 to decide to stop having contact with someone or something, or to refuse to help someone
Dictionary example:

She turned her back on Hollywood and went to live in Florida.

Learner example:

She gets to learn that Olivia turned her back on her past and merged totally with India through her attraction to and sympathy for the Nawab. (Certificate of Proficiency in English; C2; Catalan)

be (like) water off a duck's back
C2 If criticisms, insults, etc. are like water off a duck's back to you, they do not affect you at all.
Dictionary example:

She calls him lazy and useless, but it's like water off a duck's back.

Learner example:

The main lesson I have learned is by looking at some people who have lived alone for most of their life and faced with neither contradiction nor argument, they stay in their ivory tower, so sure of their opinions that whatever you say is like water off a duck's back. (Certificate of Proficiency in English; C2; French)

back · adjective always before noun /bæk/
back
A2 at or near the back of something
Dictionary examples:

a back door/garden

the back page/seat

I put it in the back pocket of my jeans.

Learner example:

There are two movies, but one is for adults so we will see "The back garden". (Preliminary English Test; B1; Spanish)

back road/street
C1 a very small road or street that goes behind or between buildings
Dictionary example:

We wandered through the back streets, looking for Tommy.

Learner example:

From the museum you have to walk across a pedestrian street, through an unspoiled district, where a jumble of narrow back streets retain old-world characters. (Certificate in Advanced English; C1; French)

back · verb /bæk/
back (sth) away/into/out, etc.
C2 to move backwards or drive backwards
Dictionary examples:

She saw he had a gun and backed away.

He backed into a wall when he was trying to park.

Learner example:

When he backed out of the [car park] he almost crashed into another car. (Certificate of Proficiency in English; C2; German)

back
C2 T to give support or help to a person, plan, or idea
Dictionary examples:

He backed Mr Clark in the recent election.

Parents backed the idea by more than two to one.

Learner example:

Of course, without [the] people wh[o] are backing the leader in his fight, he could not achieve his success. (Certificate of Proficiency in English; C2; Polish)

back off
C2 to move away from someone, usually because you are afraid
Dictionary example:

I saw he had a knife and backed off immediately.

Learner example:

Mad Dog would kill him if he tried to back off. (Certificate of Proficiency in English; C2; Portuguese)

back out
C2 to decide not to do something you had planned or agreed to do
Dictionary example:

Nigel backed out at the last minute, so we had a spare ticket.

Learner example:

When the other person backs out, then what will you do? (Certificate of Proficiency in English; C2; Dutch)

back up sb or back sb up (SUPPORT)
B2 to support or help someone
Dictionary example:

My family backed me up in my fight for compensation.

Learner example:

These courses seem to have been popular perhaps because the teacher of these courses was there to back up and help the students. (First Certificate in English; B2; Greek)

back up sb or back sb up (TRUTH)
C2 to say that someone is telling the truth
Dictionary example:

Honestly, that's exactly what happened - Claire'll back me up.

Learner example:

Was I obliged to leave her [to] live such a lie and back her husband up [in] the double life he was living? (Certificate of Proficiency in English; C2; Greek)

back up sth or back sth up
C2 often passive to prove that something is true
Dictionary example:

His claims are backed up by recent research.

Learner example:

To back up this claim, the case of children who have grown up in orphanage houses is often cited. (Certificate of Proficiency in English; C2; Japanese)

back up (sth) or back (sth) up
B2 to make an extra copy of something that is held on your computer
Dictionary example:

Always back up any music you download in case your computer crashes.

Cambridge University Press