From Ancestry on name origins:
English: status name from Middle English knyghte ‘knight’, Old English cniht ‘boy’, ‘youth’, ‘serving lad’. This word was used as a personal name before the Norman Conquest, and the surname may in part reflect a survival of this. It is also possible that in a few cases it represents a survival of the Old English sense into Middle English, as an occupational name for a domestic servant. In most cases, however, it clearly comes from the more exalted sense that the word achieved in the Middle Ages. In the feudal system introduced by the Normans the word was applied at first to a tenant bound to serve his lord as a mounted soldier.
