Crossword puzzles were, I believe, originally called cross-word puzzles, making it clear that they were constructed from words crossing each other. The designations "down" and "across" very clearly come from the directions in which the words run, especially since "across the page" in reference to words is understood to mean "from left to right" (in English, at least).
I've removed the existing clause rather than replace it with this trivial etymology.
Thanks, however, for adding the crossword sense. This sort of filling in missing pieces is what Wiktionary is all about
-dmh 20:44, 13 Mar 2004 (UTC)
Where is the pronunciation "acrost" used? I heard the BBC's Owen Bennett-Jones use it. 22.214.171.124 11:14, 4 January 2014 (UTC)