• Naff off : Get lost, go away (used as imperative). 
I told him to naff off because he was making the situation worse.
  • Nag at: Repeatedly criticize someone verbally. 
Rajesh has a bad habit of nagging at everyone.
  • Nail down: Succeed in getting something, achieve.
They nailed down the agreement after a very long discussion.
  • Nerd out: Discuss something in great detail.
The professor liked the project so much that he had to nerd out the entire design.
  • Nip off: Go somewhere quickly.
I will just nip off and get the milk from the nearest store.
  • Open up: Start to talk freely about something.
Being an introvert makes him hard to open up with strangers. 
  • Open up: Open a shop or business for the day. 
The institute opens up at eight in the morning.
  • Open up: Allow goods into a market.
IMF forced India to open up it's market for foreign companies in the 1991 crisis.
  • Operate on: Perform surgery.
The most experienced surgeons are operating on her right now.
  • Opt for: Choose.
Many students opt for any career without thinking it through under family pressure.