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

Nail (someone) (v.): To catch (someone) *usually doing something illegal/wrong*, etc.); To bust (someone). Example: "They nailed him for shoplifting."

Nail-biter (n.) : An exciting game where the outcome is uncertain until the very end. Example: That game was a real nail biter."

Neck and neck:
Very close (almost even), as in a race. Example: "The two candidates were running neck and neck a month before the election."

Neck of the woods:
*somewhat antiquated* Area. Part of a country. Example: "What's happening in your neck of the woods?"

(To) need a hand:
To need help. Example: "Do you need a hand? (Would you like some help?)"

Neither here nor there:
Not relevant. Example: "All of a sudden he started talking about his car, a topic which was neither here nor there."

Nerd (n.): Similar to "geek", but it has a little more of a derogatory ( = negative) quality to it. Someone who is socially inept, preferring academic pursuits to social ones.

Nest egg:
Saved money. Example: "He has saved up quite a nest egg. Pretty soon he'll be able to retire."

Never mind:
Don't worry about it. Example: "Did you pick up my photos? Never mind, I'll do it myself tomorrow."

(To) nip something in the bud:
To end something at an early stage.

No-brainer(n.): Very easy question; a question/situation/dilemma which has an obvious/easy solution. Example: "Well, if you ask me, it's a no-brainer. You should call her and apologize."

No laughing matter:
A very serious matter. Example: "Hey, why are you smiling? This is no laughing matter!"

No picnic:
Not easy. Very difficult and problematic. Example: "Let me tell you, driving in that snowstorm was no picnic."

No rush:
You don't have to hurry. Example: "P1: Do you want this done by this evening? P2: No, there's no rush. You can finish it tomorrow."

No skin off my nose:
I don't care because it doesn't affect me.

No sweat:
No problem.

No way: 1) Phrase used to say that something is definitely not going to happen. Example: "P1: Are you going to see her again? P2: No way!"; 2) Phrase of awe/disbelief. Example: "She gave you her phone number? No way!"

No wonder:
It's not surprising. Example: "He only slept for two hours last night? No wonder he's so tired."

(To) not be born yesterday:
To be experienced, knowledgeable. Example: "Of course I know that trick! I wasn't born yesterday."

(To) not have a prayer: To not have/stand a chance. Example: "Your team? They don't have a prayer or winning."

Not in the least:
Not at all. Example: "P1: Were you surprised that he failed the FCE? P2: Not in the least."

Not likely:
Probably will not happen. Example: "P1: You think George will learn a lesson from this? P2: Not likely."

(To) not like the looks of (someone/something): To not like the way something looks because you think it might lead to something negative. Examples: "I don't like the looks of those clouds." (because they might bring rain), "I don't like the looks of those kids." (because they look like they might cause trouble).

Not much of:
Pretty bad. Example: "I'm not much of a dancer."

(To) not put (something) past (someone): To believe that someone is capable of doing something. Example: "Would he tell the police? I wouldn't put it past him!" (Yes, I believe that he is capable of doing this.)

Now and then:
Occasionally. Now and again.