Apparently the term “Maundy Thursday” comes from the Latin phrase “mandatum novum” meaning “new commandment.” The reference is to John 13, which features the story of Jesus washing the disciples’ feet, followed by his statement about a new commandment he has given them, to love one another.
We actually reached this passage in my class on the Gospel of John yesterday, and had an interesting discussion about whether this commandment is “new,” and if so, in what sense.