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

Mag (n.): Short form for "magazine".

(To) make a beeline for (somewhere):
To head directly to (somewhere). Example: "Whenever he comes into the cafeteria, he makes a beeline for the grilled vegetables."

Make a big deal about (something) (v.): To make (something) seem very important. Example: "I don't understand why he's making such a big deal about this."

(To) make a bundle:
To make a lot of money (one time). Example: "I made a bundle when I sold my Microsoft stock last month."

Make a go of (something) (v.): To succeed in/with (something).

Make a killing: To make a lot of money. Example: "My uncle made a killing selling Chilean wine in Asia."

(To) make a long story short:
To bring a story to an end; To sum things up.

(To) make a pass (at someone):
To make romantic advances; to hit on (someone). Example: "Karl was fired because he made a pass at his co-worker Fiona."

(To) make believe:
To pretend. Example: "When your friends come, let's make believe ( = pretend) we don't know each other."

Make-believe (adj.): Imaginary; Not-real. Example: "A make-believe world".

(To) make ends meet:
To have enough money to pay one's basic expenses; to barely get by. Example: "This city is so expensive that it's hard to make ends meet sometimes."

(To) make good money:
To make a lot of money (regularly). Example: "Shawn doesn't like his job, but he makes good money."

(To) make light of something:
To treat something as if it were trivial or unimportant. Example: "Don't make light of the situation. It's more serious than you think."

(To) make life miserable for someone:
To cause someone lots of problems. Example: "Patricia's boss is making life miserable for her."

(To) make up one's mind:
To make a decision. Example: "I've made up my mind. I'm moving to Costa Rica."

(To) make oneself at home:
To feel as comfortable as one would being at home. Example: "During your visit, just make yourself at home."

(To) make someone's head spin:
To make someone dizzy or disoriented. Example: "All that alcohol made my head spin."

(To) make something from scratch:
To make something by starting with the basic ingredients. Example: "P1: Did you bake that cake? P2: No, I made it from scratch."

Man: A colloquial way guys (especially male friends) address each other; Buddy. Example: "Man, I have to tell you what happened to me last night!", "Listen, man, I don't know what you're talking about."

Maxed out (adj.): Having reached its limit (often used to speak about credit cards). Example: "My credit card has been maxed out for the past year."

(To) meet someone halfway:
To compromise with someone. Example: "They settled the argument by deciding to meet each other halfway."

Mellow out (v.): To relax.

(To) mention something in passing:
To mention something casually. Example: "She mentioned something in passing about going to check out the new Wes Anderson movie tonight."

Make waves (v.): To cause a commotion, cause trouble. Example: "Jim's a very docile person. He's not one to make waves."

(The) middle of nowhere:
A very isolated place. Example: "Our car broke down in the middle of nowhere. The nearest town was 100 miles away!"

Milk (something): To exploit (something). Example: "She was milking her 15 minutes of fame for all it was worth."

(To) mind one's own business:
Not to interfere/ get involved in the business of others. Example: "Sometimes, it's best to mind your own business."

Money talks:
Having money helps one get things done.

(There's) more than meets the eye:
(Something is) more complicated/more interesting than it seems. Example: "There's more than meets the eye when it comes to Maria. = Maria is more interesting (or complicated, depending on the context) than she appears."

(To) move up in the world:
To increase one's standing socially, etc.; to become successful. Example: "I'm not interested in moving up in the world at the expense of other people."

Munchies (n.pl): Chips and other types of junk food. Example: "I picked up some munchies on my way from work."

(A) must:
A necessity. Example: "In Los Angeles, having a car is a must."