Is there a way I can have Word consider "annus horribilis" to be spelled correctly, but not just the word "annus" on its own? I've tried using non-breaking spaces but to no avail. There's almost certainly other examples of phrases like this where the individual words wouldn't be correct on their own, so surely Word can deal with this? Then again it seems like in order for terms like "per se", "status quo" and "vice versa" to be not flagged out of the box it actually accepts "se", "quo" and "versa" on their own as words, even though they're not even valid in the official (SOWPODS) scrabble dictionary that contains all sorts of obscure 2 and 3 letter words!

Go to the Office button, choose Word Options and under Proofing choose Custom Dictionaries. Select the first option - "Edit Word List" and add your word to the list

Well obviously that was the first thing I tried. But Word still thinks both "annus" and "horribilis" are misspelled words.