Let the cat out of the bag    
          : Accidentally expose the secret

Leave someone's high and dry
          : Leave someone completely alone

Lose the head
          : Can not control the temper anymore

Lay off
          : Terminate the employment

Live from hand to mouth
          : Live with only little money. Just enough to survive

Lemon
          : Defective

Long in the tooth
          : Too old to perform work

Lay by
          : Save something for future use

Lost train of thought
          : Forgot what you were talking about

Larger than life
          : Unique, much better than normal