We tend to call these "parts" (the four parts would be writing, reading, definition, and tone). So yes, you can set yourself to just do definitions in either "temporary parts study" (web) or "advanced study" (iOS) and keep reviewing to see all the definition items, even getting into those that are not due.

Yes, you can study a ton of definitions until you get the ones which are not due and mark them wrong in order to bring them back into shorter-term reviews.

A couple users have been reporting a few problems getting the two-devices-different-parts strategy to work well (although I haven't been able to reproduce it), so I would try it with small amounts of studying before syncing first a few times to make sure it's reliable enough for you and you're not going to lose a bunch of studying.