Here is our list of American idioms that start with "L":

(A) lady-killer:
A handsome man; a man who charms women. Example: "He thinks of himself as quite the lady-killer. Unfortunately for him, women don't see him that way."

Laid-back (adj.): Relaxed, easy-going. Example: "I like Tom. He's really laid-back."

Last but not least:
Last in order but not last in importance. Example: "Last but not least, I'd like to thank my parents."

Last ditch (adj.):
Final (*has a slight connotation of "desperate"*). Example: "They made a last-ditch effort to win the game, but came up short."

(To) lay a finger on someone:
To touch someone even very slightly. Example: "If you so much as lay a finger on him, you will be in trouble."

(To) lay low:
SEE "KEEP A LOW PROFILE"

(To) leave a bad taste in someone's mouth:
To leave a negative impression on someone. Example: "The experience left a bad taste in my mouth."

(To) leave someone high and dry:
*somewhat antiquated* To leave someone helpless.

Lame (adj.): Inadequate; Bad. Example: "That's the lamest excuse I've ever heard."

Last-ditch (adj.): Final, desperate. (Often used with the words "effort", "attempt", etc.) Example: "He made a last-ditch effort to catch up to the front-runner."

Later: Short for "See you later."

Laugh (one's) head off: To laugh very hard. Example: "I laughed my head off throughout the whole movie."

Leave a bad taste in (someone's) mouth: Leave (someone) with bad feelings. Example: "That whole experience left a bad taste in my mouth."

(To) leave someone alone:
To stop bothering someone. Example: "Leave me alone! I don't want to talk to anyone."

Leave someone hanging: To not help someone when they ask for help, when they're in trouble. Example: "Don't leave me hanging... I'm counting on you!"

Legit (adj.): Short for "legitimate".

Lemme: Short for "let me".

Letdown (n.): Disappointment. Example: "I was sure that my team would win, but they lost. What a letdown!"

(To) let off steam:
To release energy or anger. Example: "P1: Victor went drinking, and got into a fight. P2: That's OK, he's just letting off a little steam."

Let (someone) have it : To attack someone (physically or verbally) with force. "Let them have it" is often shortened as "To let 'em have it" Example: "After the boys broke Mr. Smith's window, he came out and really let 'em have it."

(To) let someone off the hook:
To release someone from responsibility. Example: "Natalie said she didn't want to wash the dishes, but her mom didn't let her off the hook."

(To) let something slide:
To neglect something. To ignore something. Example: "I'm going to let it slide this time, but next time be more careful!"

(A) lift:
A ride. Example: "She gave me a lift to the airport."

Lighten up (v.): To relax; to not take things too seriously. Example: "You gotta learn to lighten up a bit!"

Little by little:
Slowly, gradually. Example: "Little by little she started to like living in New York City."

(A) little off:
Not quite even, normal. Example: "There was something a little off about the way she was behaving."

(To) lock horns:
To argue; to have a dispute; to disagree. Example: "Peter and his counterpart in France locked horns about how to implement the new regulations."

(To) look the other way:
To ignore something on purpose. Example: "In some countries, customs officials can be paid to look the other way."

(A) long shot:
Something that has a slim (small) chance of happening. Example: "They might win, but it's a long shot."

(To) lose (someone):
This is often used when someone is chasing someone OR being chased by someone. If you're being chased by someone and you manage to get away you can say "I lost him!" (I evaded him.) The person chasing you can say the same thing "I lost him." (He got away.)

(To) lose one's temper:
To become angry. Example: "He has a short fuse and loses his temper quite often."

(To) lose one's train of thought:
To forget what one was thinking/ talking about. Example: "What was I saying? I lost my train of thought."

Loser (n.): A person who fails at everything s/he tries/does in life. *not a very nice thing to say to someone!

Lost in thought:
Busy thinking. Example: "I called out to her three times, but she was lost in thought."

Lousy (adj.): Terrible. Example: "She's a lousy singer!"

Lowball, low-ball (v.): To (deliberately) underestimate or make an offer for something that is significantly below its fair value. Example: "They tried to lowball me, but I knew how much they paid the guy before me."

(To) lower one's voice:
To talk more softly. Example: "Lower your voice, my parents are asleep."

(A) lucky break:
Good luck, good fortune. Example: "I was supposed to speak at the meeting today, but I found out it was cancelled. What a lucky break!"