Some words in our language are in variation. This means that you can spell them in more than one way and still be right. The only thing you have to be careful of is using just one form of the spelling in each document. Using either form throughout is fine, but never both. The easiest way to sort this out in a long document is to do a ‘find/replace’. Publishers will often have a style guide which says which they prefer so that all their titles are consistent.
Here are some common examples:
Here are some others I’ve come across:
Sometimes variations happen because of influences from other languages and cultures, sometimes it’s just modernisation (modernization?), others have always been in contention.
Can you think of any more examples?
As always, I’d be very interested to hear if this is something you’ve come across and do please share if you’ve found this helpful! Thanks for reading!