The word “Maundy” is derived from the Latin word mandatum, or “mandate.”
This word is used in the Latin text for John 13:34:
“Mandatum novum do vobis ut diligatis invicem sicut dilexi vos.”
Or, in English:
“A new commandment I give unto you, That ye love one another; as I have loved you.”
Holy Thursday is thus sometimes called Maundy Thursday because it was on this day that Christ gave us the new commandment–the new mandate–to love one another as he loves us.