Forum Moderators: not2easy
To answer this as such: by using just CSS: not as far as I know. You can be hovering over multiple items at the same time though.
By using javascript you might be able to fake the effect you seek.
element a and element b - but there are many situations when it can easily be done using pure css. If this is the same issue as in your earlier question about drop down menus then it is entirely possible to do this using pure css and no scripting. A search on "css drop down menu" and variations will bring up lots of examples.
If not the same situation as your earlier post, then post some code so possibilities can be explored.