Young Reddish Blonde Girl Outside With A Knight's Helmet And A Horse

The word knight, from Old English cniht ("boy" or "servant"), is a cognate of the German word Knecht ("servant, bondsman"). This meaning, of unknown origin, is common among West Germanic languages (cf: Old Frisian kniucht, Dutch knecht, Danish knægt, Swedish knekt, Middle High German kneht, all meaning "boy, youth, lad", as well as German Knecht "servant, bondsman, vassal"). Old English cniht had no particular connection to horsemanship, referring to any servant. A rādcniht (meaning "riding-servant") was a servant delivering messages or patrolling coastlines on horseback. Old English cnihthād ("knighthood") had the meaning of adolescence (i.e. the period between childhood and manhood) by 1300.
A narrowing of the generic meaning "servant" to "military follower of a king or other superior" is visible by 1100. The specific military sense of a knight being a mounted warrior in the heavy cavalry emerges only in the Hundred Years' War. The verb "to knight", i.e. to make someone a knight appears around 1300, and from the same time, the word "knighthood" shifted from "adolescence" to "rank or dignity of a knight".
In this respect English differs from most other European languages, where the equivalent word emphasizes the status and prosperity of war horse ownership. Linguistically, the association of horse ownership with social status extends back at least as far as ancient Greece, where many aristocratic names incorporated the Greek word for horse, like Hipparchus and Xanthippe; the character Pheidippides in Aristophanes' Clouds has his grandfather's name with hipp- inserted to sound more aristocratic. Similarly, the Greek ἱππεύς (hippeus) is commonly translated "knight"; at least in its sense of the highest of the four Athenian social classes, those who could afford to maintain a warhorse in the state service.
An Equestrian (Latin, from eques "horseman", from equus "horse") was a member of the second highest social class in the Roman Republic and early Roman Empire. This class is often translated as "knight"; the medieval knight, however, was called miles in Latin, (which in classical Latin meant "soldier", normally infantry).