Someone asked today in a comment whether “documentor” or “documenter” is correct. The correct word is “documenter.” The question got me wondering, though, about another spelling dilemma: “adviser” or “advisor.”
According to the Cambridge Guide to English Usage (Pam Peters, 2004):
Both these spellings are in current use, though adviser is the dominant spelling in both the US and the UK. The ratio in American data from CCAE is 20:1 and in British data from the BNC it’s 6:1. Curiously, advisor is sometimes said to be “the American spelling.” Whatever its past, advisor is registered alongside adviser in major British, American, Canadian and Australian dictionaries.
The Columbia Guide to Standard American Usage tersely states,
Both spellings are Standard.
For this word, my preference is to go with common usage and write “adviser.”