E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
improperly Guerilla wars, means a petty war, a partisan conflict; and the parties are called Guerillas or Guerilla chiefs. Spanish, guerra, war. The word is applied to the armed bands of peasants who carry on irregular war on their own account, especially at such time as their Government is contending with invading armies.
The town was wholly without defenders, and the guerillas murdered people and destroyed property without hindrance.Lessing: United States, chap. xviii. p. 676.