Nassau

a type of wager in which the first nine holes, the last nine holes and the total for 18 holes are three separate bets

 

NC     

scoreboard abbreviation for "No card", meaning that the player did not turn in a scorecard
 

Neck 

the part of the club into which the shaft is inserted (also "hosel")

Net

a players score after a handicap has been applied
 

Never up, never in

refers to the obvious fact that if a putt does not have enough speed to reach the hole it can't go in

Nineteenth hole

the bar or lounge after a round of golf (also "19th hole")

Ninety degree rule

 a practice where golf cars are allowed to drive on the fairway, or away from the cart paths, only perpendicularly (90°) to the hole being played, usually for the purpose of decreasing wear and tear on the turf or for the reason of fragile grass condition, etc. (also "90° rule, 90 degree rule")

Nutted
hitting it squarely and on the sweetspot (also "flushed, in/on the screws")