noun (n)

• an irritating or obnoxious person(noun.person)

  Synonym:
  varmint
  

  source: wordnet30
• any of various small animals or insects that are pests; e.g. cockroaches or rats(noun.animal)

  Example:
  Cereals must be protected from mice and other vermin.
  He examined the child's head for vermin.
  Boys in the village have probably been shooting vermin.
  

  source: wordnet30
• An animal, in general.(noun)

  source: webster1913