Use Apache's mod_alias module to perform a permanent redirect like:
RedirectPermanent / "http://world wide web.example.com/"
Put the redirect within the blank subdomain's virtualhost block or root level
The trailing / on "http://world wide web.example.com/" is vital.
I'll add an alternative choice here that I have accustomed to permit other specific hosts too. For instance should you wanted a dev.example.com along with a blog.example.com site additionally for your world wide web.example.com site, put this inside your root level .htaccess file:
RewriteCond % . RewriteCond % !^www.example.com RewriteCond % !^dev.example.com RewriteCond % !^blog.example.com RewriteRule (.*) http://world wide web.example.com/$1 [R=301,L,QSA]