after much wondering over many years, recently got around to googling "maunday thursday origins" and discovered that "maunday" is simply a corruption of the Latin word "Mandatum", meaning "command". so called because at the last supper, which is celebrated today, Jesus washed his disciples feet and mandated them to similarly wash one anothers' feet. it seems a latin hymn was often sung at early holy thursday services, and the chorus began with a form of mandatum, and so the day itself began to be called maunday thursday.
[edit: Val notes that "maunday" should be "maundy". i think she is probably right, as a search on google for "maunday thursday" returns 6,880 results (for an example, see this page: http://www.sacred-texts.com/neu/eng/osc/osc07.htm) and "maundy thursday" returns 225,000 results. but there is something both comforting and disturbing about being wrong with 6,879 other people]
off to a church board meeting tonight. great board. wonderful group of disciples who keep trying to outdo one another in service. they've got the edge on me, in my book.