It appears that with Version 10 Mathematica only allows the spell checking of an entire notebook. I would like to spell check a single Text cell, which I guess is more of a suggestion because that option has never been available.

However, pre-Version 10 it was possible to check a single word in Text cells by placing the cursor after a word and using Ctrl+K. This would bring up a list of suggested words (and in Version 9 an error warning). I found this extremely convenient but it seems to be no longer available. (It brings up a black square at the top left corner of my screen.)

It would be very useful if Mathematica had more convenient spell checking, especially in the area of using it as a technical communication medium.