I use some old English words in my books so I thought it would be a good idea to have a little glossary of them here. The medieval words are what you might hear typically at a Renaissance fair. Medieval England went through a transition of languages from the Saxons to the Normans until Middle English became popular and closely resembles what we speak now. You would most likely recognise the words from Shakespeare's work.
Demesne - An estate or part of an estate
Destrier - A strong breed of horse, usually used for war.
Gambeson - A padded jacket worn under chanmail to protect the wearer.
Hauberk - Chainmail
Helm - A helmet
Rouncey - A horse. Usually used to refer to an ordinary horse, used for all purposes.
Sennight - A week
Surcoat - A long garment, typically worn during the crusades, over chainmail. Often sleeveless, they usually reached down to the knees. Women also wore longer versions over their other garments.
Villein - A person who held loyalty to their lord. Villeins had some rights and were considered partially free.
Garderobes - Toilets
Solar - Bedroom/Area for the lady and lord of the castle to relax in.
Bliaut - Usually a loosely draped gown with long sleeves.