How did this word get the /O:/ vowel? By its spelling, I would expect it to be /o:/ like 'road'. Anyone know?
Etymology of 'broad'
This is probably due to irregularities in the Great Vowel Shift which occurred, in particular before /t/ and /d/ in more common words. In many more common words the GVS did not really occur as expected but rather was incomplete. Furthermore, there was irregular shortening of vowels in many cases before /t/ and /d/. The two things explain many of the words with vowels other than those which one would expect which had /E:/, /O:/, /e:/, or /o:/ in them in Middle English