noun (n)

• defensive structure consisting of walls or mounds built around a stronghold to strengthen it(noun.artifact)

  Synonym:
  munition
  

  source: wordnet30
• the art or science of strengthening defenses(noun.cognition)

  source: wordnet30
• the addition of an ingredient for the purpose of enrichment (as the addition of alcohol to wine or the addition of vitamins to food)(noun.act)

  source: wordnet30
• The act of fortifying; the art or science of fortifying places in order to defend them against an enemy.(noun)

  source: webster1913