Here is a list of idiomatic expressions using the letters K and L.
Keep your nose to the grindstone
To keep your nose to the grindstone is to apply yourself conscientiously to your work.
Keep a wolf from the door
To keep a wolf from the door is to earn enough to avoid starvation.
Kick the bucket
To kick the bucket is to die. This is a euphemism.
Kill two birds with one stone
To kill two birds with one stone is to accomplish two goals with a single effort.
Knee jerk reaction
An immediate emotional reaction often triggered by an event or a statement to which the reacting person is highly sensitive.
Know the ropes
If you know the ropes, you know how an organization or establishment works.
Know which way the wind blows
To understand what is the most important thing to do under the conditions at hand.
Labor of love
Work undertaken for the pleasure of it, or for the benefit of a loved one.
Last but not the least
This is used to say that the last item in a list is not necessarily the least important.
An object that attracts ridicule or laughter
Learn the ropes
To learn the ropes is to learn the way something works.
Leave no stone unturned
When you leave no stone unturned, you make every possible effort to do something.
Let the cat out of the bag
To let the cat out of the bag is to reveal a secret.
Level playing field
In a level playing field, all players have to play by the same rules. That means nobody has an advantage over the others.
To lie low is to keep a low profile.
Living on borrowed time
If somebody is living on borrowed time, they are not expected to live much longer.