noun (n)

• a fee charged in advance to retain the services of someone(noun.possession)

  Synonym:
  consideration
  

  source: wordnet30
• a person working in the service of another (especially in the household)(noun.person)

  Synonym:
  servant
  

  source: wordnet30
• a dental appliance that holds teeth (or a prosthesis) in position after orthodontic treatment(noun.artifact)

  source: wordnet30
• One who, or that which, retains.(noun)

  source: webster1913