back down
to decide not to do something because of opposition, or because of pressure from authorities

back out
If you back out of something like an agreement or a deal, you decide not to follow through on it.

back up
to make an extra copy of digital information on disc, flash drive, external hard drive, etc. in case the original data is lost

back up
If you back up what you say, you use evidence or examples to show that it's true.

bail out
to help out someone or something that's in serious trouble, especially financial trouble

bail out  
to give money to a court so that an accused person doesn't have to stay in jail until their trial begins

bank on
If you bank on something happening or someone doing something, you depend on it or count on it.

base on
to use specific information, ideas or past experiences as a basis for making a decision

base on
to use something as source material

bear on
to have relevance to, or influence on, something

bear out
to show that someone is correct or that something is true

beat up
to hurt someone by punching, kicking or hitting them with a hard object

become of
If you ask what has become of someone you haven't seen or heard from for a long time, you want to know what's happened to them.

beef up
to make something stronger or more powerful

begin with
If an activity or an event begins with something, that's the first thing that happens.

believe in
If you believe in something, you're sure that it's true or it really exists.

belong to
If something belongs to a person, it is owned by that person.

bend down
to move the upper part of your body forwards and downwards

bet on
to be sure that something will happen

bite off
to separate something from whatever it's attached to by biting it

black out
to lose consciousness

blow away
to surprise or amaze someone

blow out
If a flame blows out, it goes out because someone blows on it or because of the wind.

blow up  
If you blow up something, you use explosives to damage or destroy it.

blow up  
to fill with air or gas in order to inflate something

blow up
to make a photograph larger

border on
If something like an action or an attitude borders on something more extreme, it is close to being that extreme.

bow out
to resign from a job, or to end a career, usually after a long time

break down
If a machine or a vehicle breaks down, it stops working because of a mechanical problem.

break down
If someone breaks down, they start crying.

break into
If someone breaks into a building or a vehicle, they force their way in, usually to steal something.

break out
to escape from somewhere like a jail or a detention centre

break up
If you break up with your boyfriend or girlfriend, you end your relationship with him or her.

breathe in
to fill your lungs with air by drawing it in through your nose or mouth

breathe out
to push air out from your lungs through your nose or mouth

brighten up  
to make a place or a thing look more cheerful and more lively

brighten up  
to become happier and feel more cheerful

bring about
If you bring about something, you cause it to happen or you make it happen.

bring back
to bring something with you when you return from somewhere

bring back  
to make something from the past come back, such as a memory, a feeling, an idea, etc.

bring down
to cause a government or a leader to lose power

bring forward
to change the date or time of an event so that it happens earlier than originally planned

bring off
to succeed in doing something that's difficult

bring on
to cause something like an illness or a painful emotion

bring out  
to release a new product

bring out  
to make a quality in someone or something show itself

bring up
If you bring somebody up, you raise them from childhood to young adulthood.

bring up
to raise a new topic for discussion, or to mention a particular subject or issue in a conversation

brush up
to revise your knowledge of something that you learned in the past

buckle up
to fasten a seatbelt in a car or on a plane

bugger off
If you tell someone to bugger off, you're telling them to go away in a very impolite and aggressive way.

build on
to add to what you've already succeeded in doing

build on
to add a new section to a house or a building

build up  
to work at something and make it get stronger or bigger

build up  
to gradually increase

bump into
to meet somebody by chance

burn down
If something like a building or a forest burns down, it's completely destroyed in a fire.

burn out  
If a fire burns out, it slowly dies down until it stops burning altogether.

burn out  
to work too hard and suffer from physical and mental exhaustion

butt in
to start talking when somebody else is already talking

butt out
If you want to tell someone quite forcefully to mind their own business, you can tell them to butt out.

butter up
to say nice things to someone before asking them to do something for you or to give you something

buy out
to buy somebody's share of a company or a partnership in order to take control of it

buy up
to buy all or a lot of something that is in limited supply