wordsward

Old English weardian is to watch, to guard, to keep, to protect; the noun weard is the watching itself. The Norman conquest sent the same Germanic root back across the Channel and returned it as guard, so English carries the word twice, once early and Germanic and once late and French, and uses the two for different registers.

The noun went somewhere the verb did not. In law a ward is not the thing that protects but the person protected: a minor or an incapacitated adult placed under a guardian or a court. That sense runs out of feudal wardship, where custody of a minor heir's lands, of the heir, and of the heir's choice of marriage partner were rights that got sold to the highest bidder or granted as a favour. Henry VIII sponsored the Statute of Uses in 1535 to protect his income from wardship and established the Court of Wards and Liveries in 1540. The court lost its function in 1646 with the abolition of feudal tenure in England and Wales, and was abolished in 1660.

The word then travelled with the common law. In Australia, New Zealand and the United States a child is a ward of the court; in Ireland and the United Kingdom, a ward of court with no article; in Canada, a permanent ward, except in Ontario, which says Crown ward. In France a pupille de l'État is a minor under the responsibility of the state.

Inference — one root, two ends that face each other. The horseshoe over a door wards. The child inside the house is a ward. English has kept both without ever needing to notice.