knight in the Middle Ages, a man who served his sovereign or lord as a mounted soldier in armour; a man raised by a sovereign to honourable military rank after service as a page or a squire.

In the UK, a knight is a man awarded a non-hereditary title by the sovereign in recognition of merit or service and entitled to use the honorific ‘Sir’ in front of his name.

Knight is also a dated term for a member of the class of equites in ancient Rome, or a citizen of the second class in ancient Athens (called hippeus in Greek), seen in comparison with medieval knights.

In chess, a knight is a piece, typically with its top shaped like a horse's head, that moves by jumping to the opposite corner of a rectangle two squares by three. Each player starts the game with two knights.

The word is recorded from Old English (in the form cniht, denoting ‘boy, youth, servant’) and is of West Germanic origin.
knight errant a medieval knight wandering in search of chivalrous adventures.
Knight of Columbus a member of a society of Roman Catholic men founded at New Haven, Connecticut, in 1882.
Knight of the Round Table a member of the brotherhood of knights who were followers of King Arthur.
Knight of the Rueful Countenance another name for Don Quixote.
knight of the shire a gentleman representing a shire or county in Parliament, originally, a parliamentary member chosen from those holding the rank of knight.
knight service in the Middle Ages, the tenure of land by a knight on condition of performing military service.

See also knights, white knight.