- La-di-da
- Labour of love
- Lackadaisical
- Ladies' room
- La dolce vita
- Lager frenzy
- Laid out in lavender
- La-la land
- Lamb to the slaughter
- Lame duck
- Land-lubber
- Land of nod
- Lantern-jawed
- Lardy-dardy
- Lark about
- Last but not least
- Last straw
- Latin Phrases
- Laugh like a drain
- Laughing-stock
- Laurels
- law is an ass
- Lay it on with a trowel
- Lead balloon
- Lead-pipe cinch
- Learn the ropes
- Left hand doesn't know what the right hand is doing
- Left in the lurch
- Legend in one's own lifetime
- Leopard cannot change its spots
- Less is more
- Less or fewer?
- Let a thousand flowers bloom
- Let bygones be bygones
- Let not poor Nelly starve
- Let not the sun go down on your wrath
- Let or hindrance
- Let sleeping dogs lie
- Let the cat out of the bag
- Let them eat cake
- Let there be light
- Let your hair down
- Let's roll
- Level playing field
- Lick and a promise
- Lick into shape
- Lickety-split
- Lie low
- Lies, damned lies and statistics
- Life begins at forty
- Life in the 1500s – folk etymologies
- Life of Riley
- Life's not all beer and skittles
- Life's too short
- Like a butcher's dog
- Like a chicken with its head cut off
- Like a moth to a flame
- Like being savaged by a dead sheep
- Like billy-o
- Like it or lump it
- Like rearranging the deckchairs on the Titanic
- Like the clappers
- Like the Dickens
- Like turkeys voting for Christmas
- Like two peas in a pod
- Lily-livered
- Little bird told me
- Little knowledge is a dangerous thing
- Little of what you fancy does you good
- Lions led by donkeys
- Little pitchers have big ears
- Live long and prosper
- Living daylights
- Living off the fat of the land
- Living on borrowed time
- Lo and behold
- Load of cobblers
- Load of codswallop
- Loaf of bread
- Local derby
- Lock stock and barrel
- Long arm of the law
- Long in the tooth
- Look before you leap
- Loose cannon
- Loose lips sink ships
- Lose face
- Lose your marbles
- Love is blind
- Love that dare not speak its name
- Loved-up
- Lovey-dovey
- Lunatic fringe