1. [n]  action intended to nullify the effects of some previous action
2. [n]  action intended to keep a country politically neutral or exclude it from a possible war; "the neutralization of Belgium"
3. [n]  a chemical reaction in which an acid and a base interact with the formation of a salt; with strong acids and bases the essential reaction is the combination of hydrogen ions with hydroxyl ions to form water

NEUTRALISATION is a 14 letter word that starts with N.