Weird’s history is a pretty odd one and it only came to have the meaning we recognise today, ‘strange’ or ‘bizarre’, relatively recently.
Going all the way back to Proto-Indo-European, we find *wert-, meaning ‘to turn’ or ‘to bend’, which is related to Latin word versus. This then developed in Proto-Germanic as *wurthiz which has relatives in Old High German, wurt, and Old Norse, urðr. It then entered Old English as wyrd. However, by this time, the word no longer meant ‘to turn’ or ‘to bend’ but ‘fate’, ‘destiny’ or literally ‘that which comes’, in a similar way to how turn into can mean ‘become’ now.
This sense of ‘fate’ or ‘destiny’ is found as far back as Beowulf:
Gæð a wyrd swa hio scel.
(Fate goes ever as fate must.)
Hie wyrd forsweop on Grendles gryre.
(Fate sweeps them away into Grendel’s clutches.)
In the 1400s, weird meant having the power to control fate, or it was the personification of fate as in the three Fates of Greek and Roman mythology. In Chaucer’s The Legend of Good Women from c.1385, weird is clearly being used as an animate noun:
The werdys that we clepyn destene Hath shapyn hire that she mot nedis be Pyetous sad.
(The weirds that we call destiny have determined that she must necessarily be piously solemn.)
By 1625, the use of weird to mean ‘witch’ was quite common and the first record of weird being used as an adjective stems from this sense. Perhaps the most famous use of weird to mean ‘witch’ is found in Shakespeare’s Macbeth in the characters of the weird sisters, who were, of course, witches and able to foresee the future.
After Shakespeare’s weird sisters, weird as an adjective expanded into other contexts but the modern sense of ‘strange’ didn’t develop until the 19th century. The last step probably came about through the idea of something weird being ‘unearthly’ and therefore ‘strange’ or the portrayal of weird sisters as frightening, odd-looking and disturbingly different.