What does Boxing Day have to do with boxing?
early 15c., "pertaining to metaphysics," from methaphesik (late 14c.) + -al, and in part from Medieval Latin metaphysicalis, from Medieval Latin metaphysica (see metaphysics). It came to be used in the sense of "abstract, speculative" (e.g. by Johnson, who applied it to certain 17c. poets, notably Donne and Cowley, who used "witty conceits" and abstruse imagery). Related: Metaphysically.