something that you say in order to advise someone to think about possible problems before doing something.

If you're thinking of buying a house, my advice is, look before you leap.

• bargaining chip
• barge in
• barking up the wrong tree
• bark is worse than bite
• bark is worse than their bite
• bar none
• basket case
• bat an eye
• bat an eyelash
• bat an eyelid
• bat around
• bat around something
• bat for the other side
• batten down the hatches
• battle lines are drawn
• battle of nerves
• battle of the sexes
• battle of wills
• battle of wits
• be a athlete in the making
• be a [athlete/star/writer etc.] in the making
• be a barrel of laughs
• be a bed of nails
• be a bit much
• be a blessing in disguise