Weird what you stumble across in SharePoint! There is no end to finding things!
Center or Centre? Organization or Organisation? Harbor or Harbour?
SharePoint 2013 search, both On Prem and Office 365, appears to have a US/UK synonym list built-in. I can't find documentation for it anywhere, but it seems to work as expected. Below a few of the words I tested. Search for one and you will find documents with the other.
My editor's spell checker marks all but one of the second terms as misspelled! It seems to like "spelt".
To see a list of these common spelling variations see https://en.wikipedia.org/wiki/American_and_British_English_spelling_differences