On more than one occasion over the past — *checks notes* — half-century, I have been moved to look up the proper spelling of the word people say when bringing a horse to a stop or expressing stoner surprise. Until fairly recently I was sternly advised that the only such word was ‘whoa’, and in no civilized context would one write ‘woah’. Meaning even though there were two available spellings for two distinct usages, there was only one proper spelling for that word regardless of the intent or context.
Over the past year or two, however, ‘woah’ seems to be gaining steam, and some sources are now grudgingly acknowledging that — as language is wont to do — we are witnessing the evolution of the spelling of that word. What does not seem to be happening, however, is any disambiguation between the spellings and definitions, and I think that is a missed opportunity. If we have two completely different usages, and a new alternative spelling is gaining legitimacy, that would be the perfect time to differentiate between the spellings and definitions, forking them into homonyms.
To that end, and in service of clarity forever more, I am advocating that ‘whoa’ continue to be used to indicate a literal or figurative command to stop, while ‘woah’ should be used to signify low-key surprise or shock. As to how to put this plan into action, just put the plan into action. When you mean stop, write ‘whoa’. When you mean wow, write ‘woah’. The word police will catch up.
— Mark Barrett