1. back down: To decide not to do something because of opposition, or because of pressure from authorities.
2. back out: If you back out of something like an agreement or a deal, you decide not to follow through on it.
3. back up (1): To make an extra copy of digital information on disc, flash drive, external hard drive, etc. In case the original data is lost.
4. back up (2): If you back up what you say, you use evidence or examples to show that it's true.
5. bail out (1): To help out someone or something that's in serious trouble, especially financial trouble.
6. bail out (2): To give money to a court so that an accused person doesn't have to stay in jail until their trial begins.
7. bank on: If you bank on something happening or someone doing something, you depend on it or count on it.
8. base on (1): To use specific information, ideas or past experiences as a basis for making a decision.
9. base on (2): To use something as source material.
10. bear on: To have relevance to, or influence on, something.
11. bear out: To show that someone is correct or that something is true.
12. beat up: To hurt someone by punching, kicking or hitting them with a hard object.
13. 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.
14. beef up: To make something stronger or more powerful.
15. begin with: If an activity or an event begins with something, that's the first thing that happens.
16. believe in: If you believe in something, you're sure that it's true or it really exists.
17. belong to: If something belongs to a person, it is owned by that person.
18. bend down: To move the upper part of your body forwards and downwards.
19. bet on: To be sure that something will happen.
20. bite off: To separate something from whatever it's attached to by biting it.
21. black out: To lose consciousness.
22. blow away: To surprise or amaze someone.
23. blow out: If a flame blows out, it goes out because someone blows on it or because of the wind.
24. blow up (1): If you blow up something, you use explosives to damage or destroy it.
25. blow up (2): To fill with air or gas in order to inflate something.
26. blow up (3): To make a photograph larger.
27. border on: If something like an action or an attitude borders on something more extreme, it is close to being that extreme.
28. bow out: To resign from a job, or to end a career, usually after a long time.
29. break down (1): If a machine or a vehicle breaks down, it stops working because of a mechanical problem.
30. break down (2): If someone breaks down, they start crying.
31. break into: If someone breaks into a building or a vehicle, they force their way in, usually to steal something.
32. break out: To escape from somewhere like a jail or a detention centre.
33. break up: If you break up with your boyfriend or girlfriend, you end your relationship with him or her.
34. breathe in: To fill your lungs with air by drawing it in through your nose or mouth.
35. breathe out: To push air out from your lungs through your nose or mouth.
36. brighten up (1): To make a place or a thing look more cheerful and more lively.
37. brighten up (2): To become happier and feel more cheerful.
38. bring about: If you bring about something, you cause it to happen or you make it happen.
39. bring back (1): To bring something with you when you return from somewhere.
40. bring back (2): To make something from the past come back, such as a memory, a feeling, an idea, etc.
41. bring down: To cause a government or a leader to lose power.
42. bring forward: To change the date or time of an event so that it happens earlier than originally planned.
43. bring off: To succeed in doing something that's difficult.
44. bring on: To cause something like an illness or a painful emotion.
45. bring out (1): To release a new product.
46. bring out (2): To make a quality in someone or something show itself.
47. bring up (1): If you bring somebody up, you raise them from childhood to young adulthood.
48. bring up (2): To raise a new topic for discussion, or to mention a particular subject or issue in a conversation.
49. brush up: To revise your knowledge of something that you learned in the past.
50. buckle up: To fasten a seatbelt in a car or on a plane.
51. bugger off: If you tell someone to bugger off, you're telling them to go away in a very impolite and aggressive way.
52. build on (1): To add to what you've already succeeded in doing.
53. build on (2): To add a new section to a house or a building
54. build up (1): To work at something and make it get stronger or bigger.
55. build up (2): To gradually increase.
56. bump into: To meet somebody by chance.
57. burn down: If something like a building or a forest burns down, it's completely destroyed in a fire.
58. burn out (1): If a fire burns out, it slowly dies down until it stops burning altogether.
59. burn out (2): To work too hard and suffer from physical and mental exhaustion.
60. butt in: To start talking when somebody else is already talking
61. butt out: If you want to tell someone quite forcefully to mind their own business, you can tell them to butt out.
62. butter up: To say nice things to someone before asking them to do something for you or to give you something.
63. buy out: To buy somebody's share of a company or a partnership in order to take control of it.
64. buy up: To buy all or a lot of something that is in limited supply.
