Thanks for the link! All true - but if I understand the OP's article right, the whole emergence of the modern word "weird" came because in Shakespeare's time,

Thanks for the link! All true - but if I understand the OP's article right, the whole emergence of the modern word "weird" came because in Shakespeare's time, the original root "wyrd" and meaning "fate" of the word were basically lost to history for most people. So contemporaries made up a new meaning "odd" when the word again got more popular through the play. Pratchett hints at this by straight-up using the old spelling, that not even in the original Shakespeare play was used - and then of course plays with both meanings, as the witches are both deeply involved with fate, but also just strange in the modern sense. Disclaimer though: Didn't read either Macbeth nor this Discworld book so far, soo ... this is just idle speculation.