Nonne macescis? - Have you lost weight?
Nosce te ipsum - Know thyself. (Inscription at the temple of Apollo in Delphi.)
Nota bene (nb.) - Note well. Observe carefully

Novus homo

A new Man; a man who was the first in his family to be elected to an office

Novus ordo saeculorum - A new order of ages
Novus ordo seclorum - A new order for the ages. (appears on the U.S. one-dollar bill)
Nulla avarita sine poena est - There is no avarice without penalty. (Seneca)
Nulla dies sine linea - Not a day without a line. Do something every day! (Apeles, Greek painter)
Nulla regula sine exceptione - There is no rule/law without exception
Nulla res carius constat quam quae precibus empta est - Nothing is so expensive as that which you have bought with pleas. (Seneca)