noun

• (historical) An infantry soldier, often of European Christian background from the Balkans as well as Eastern Europe and forcibly converted to Islam, in a former elite Turkish (Ottoman) guard (disbanded in 1826).
  "My Lord the great Commander of the worlde, Besides fifteene contributory kings, Hath now in armes ten thouſand Ianiſaries, Mounted on luſty Mauritanian Steeds, […]"
• (historical) An infantry soldier, often of European Christian background from the Balkans as well as Eastern Europe and forcibly converted to Islam, in a former elite Turkish (Ottoman) guard (disbanded in 1826).
• (figuratively) An elite, highly loyal supporter.
  "Here is a Proclamation for a Prince: that proclaims him in whoſe name it is emitted [James II of England], to be the greateſt Tyrant that ever lived in the world, and their Revolt who have diſowned him to be the juſteſt that ever was. For herein that Monſter of Prerogative is […] advanced […] to claim abſolute obedience, without reſerve of Conſcience, Religion, Honour, or Reaſon; not only that which ignorantly is called Paſſive, never to reſiſt him, not only on any Pretence, but for any Cauſe, even tho' he ſhould command his Popiſh Janizaries to murder and maſſacre all Proteſtants, which is the tender mercy and burning fervent charity of Papiſts; […]"