What is the best word for lateral translational movement in a rotorcraft?
The term I preferred was "slide"

In our NATOPS manuals, and in our trained procedures in both Search and Rescue ops, and cargo ops, in the Navy the crewman would call for us to "slide left" or "slide right" as he positioned us over the pick up point.  (Easy Left/Easy Right as we got closer to the spot).  

The FAA term "sideward hovering" suffices, but it is two words.  If you want one word, slide is about right.